gr-qc - UChicago High Energy Physics

Transcription

gr-qc - UChicago High Energy Physics
[email protected]
Nuclear Energy Density Functionals: What do we really know?
Aurel Bulgac,1, ∗ Michael McNeil Forbes,2, 1, † and Shi Jin1, ‡
1 Department
of Physics,
University of Washington, Seattle,
Washington 98195–1560,
USA
2 Department of Physics & Astronomy,
Washington State University,
Pullman, Washington 99164–2814,
USA
arXiv:1506.09195v1 [nucl-th] 30 Jun 2015
(Dated: July 1, 2015)
We present the simplest nuclear energy density functional (NEDF) to date, determined by only 4
significant phenomenological parameters, yet capable of fitting measured nuclear masses with better
accuracy than the Bethe-Weizsäcker mass formula, while also describing density structures (charge
radii, neutron skins etc.) and time-dependent phenomena (induced fission, giant resonances, low
energy nuclear collisions, etc.). The 4 significant parameters are necessary to describe bulk nuclear
properties (binding energies and charge radii); an additional 2 to 3 parameters have little influence on
the bulk nuclear properties, but allow independent control of the density dependence of the symmetry
energy, excitation energy of isovector excitations, and the Thomas-Reiche-Kuhn sum rule. This
Hohenberg-Kohn–style of density functional theory (DFT) successfully realizes Weizsäcker’s ideas
and provides a computationally tractable model for a variety of static nuclear properties and dynamics,
from finite nuclei to neutron stars, where it will also provide a new insight into the physics of the
r-process, nucleosynthesis, neutron star crust structure, and neutron star mergers. This new NEDF
clearly separates the bulk geometric properties – volume, surface, symmetry, and Coulomb energies
which amount to ∼ 8 MeV per nucleon or up to ∼ 2000 MeV per nucleus for heavy nuclei – from finer
details related to shell effects, pairing, isospin breaking, etc. which contribute at most a few MeV for
the entire nucleus. Thus it provides a systematic framework for organizing various contributions to the
NEDF. Measured and calculated physical observables – i.e. symmetry and saturation properties, the
neutron matter equation of state, and the frequency of giant dipole resonances – lead directly to new
terms, not considered in current NEDF parameterizations.
VI. Supplemental material
CONTENTS
I. Introduction
II. Static Properties
A. Form of the NEDF
B. Gradient Terms
C. Infinite Nuclear and Neutron Matter
1
4
5
6
7
III. Fitting Masses and Charge Radii
A. Discussion
B. Neutron Matter
C. Saturation and Symmetry Properties
D. Symmetry Energy and Neutron Skin Thickness
E. Neutron Drip Line
F. Charge Radii
G. Principal Component Analysis
8
9
10
11
12
12
13
15
IV. Dynamical Properties
A. Entrainment
B. Shell Effects
C. Induced Symmetric and Asymmetric Fission
D. Giant Isovector Resonances
16
17
18
19
19
V. Conclusions
Acknowledgments
∗
†
‡
[email protected]
[email protected]
[email protected]
20
21
References
21
21
I. INTRODUCTION
Calculating nuclear masses, nuclear matter and charge distributions, and dynamics in nuclear systems remains one of
the most challenging problems in quantum many-body theory.
Almost a century ago, Aston (1920) realized that a nucleus
is not quite the sum of its parts, leading Eddington (1920) to
correctly conjecture a link between nuclear masses, the conversion of hydrogen into heavier elements, and the energy
radiated by the stars. When quantum mechanics was first applied to many-body systems, Weizsäcker (1935) proposed that
an energy density approach could be effective for calculating
nuclear binding energies. This was the first instance of an
energy density functional being applied in nuclear physics,
with the fundamentals of DFT laid several decades later (Dreizler and Gross, 1990; Hohenberg and Kohn, 1964; Kohn and
Sham, 1965). Bethe and Bacher (1936) further developed
Weizsäcker’s ideas and introduced the nuclear mass formula
(known as the Bethe-Weizsäcker formula) for the ground state
energies of nuclei with A = N + Z nucleons (N neutrons and Z
Towards relativistic quantum geometry
2
Luis Santiago Ridao,
1,2
Mauricio Bellini
∗
1
Departamento de F´ısica, Facultad de Ciencias Exactas y Naturales,
Universidad Nacional de Mar del Plata, Funes 3350, C.P. 7600, Mar del Plata, Argentina.
2
Instituto de Investigaciones F´ısicas de Mar del Plata (IFIMAR),
Consejo Nacional de Investigaciones Cient´ıficas y T´ecnicas (CONICET), Mar del Plata, Argentina.
arXiv:1506.09141v1 [hep-th] 30 Jun 2015
We obtain a gauge-invariant relativistic quantum geometry by using a Weylian-like integrable
manifold with a geometric scalar field which provides a gauge-invariant relativistic quantum theory
in which the algebra of the Weylian-like field depends on observers. An example for a Reisnn¨erNordstr¨
om black-hole is studied.
I.
INTRODUCTION
The study of geometrodynamics was introduced by Wheeler in the 50’s decade in order to describe particle as
geometrical topological defects in a relativistic framework[1], and, in the last years has becoming a very intensive
subject of research[2]. However, at the present time, it is not possible to realize a consistent quantum gravity theory
which leads to the unification of gravitation with the other forces. One of the problems relies in the impossibility of
constructing a gauge-invariant and nonperturbative formalism which can describe intense gravitational fields.
It is known that in the event that a manifold has a boundary ∂M, the action should be supplemented by a boundary
term so that the variational principle to be well-defined[3, 4]. However, this is not the only manner to study this
problem. As was recently demonstrated[5], there is another way to include the flux around a hypersurface that
encloses a physical source without the inclusion of another term in the Einstein-Hilbert (EH) action, but by making
a constriction on the first variation of the EH action. En that paper was demonstrated that the non-zero flux of the
vector metric fluctuations through the closed 3D Gaussian-like hypersurface, is responsible for the gauge-invariance
of gravitational waves.
To see it, we consider the problem of a EH action I, which describes gravitation and matter
Z
R
4 √
(1)
+ Lm .
d x −g
I=
2κ
V
The first term in (1) is the Einstein-Hilbert action and κ = 8πG. Here, g is the determinant of the covariant
α
background tensor metric gµν , R = g µν Rµν is the scalar curvature, Rµνα
= Rµν is the covariant Ricci tensor and Lm
is an arbitrary Lagrangian density which describes matter. If we deal with an orthogonal base, the curvature tensor
will be written in terms of the connections: Rαβγδ = Γαβδ,γ − Γαβγ,δ + Γǫ βδ Γαǫγ − Γǫ βγ Γαǫδ .
The first variation of the action is
Z
√ δI = d4 x −g δg αβ (Gαβ + κTαβ ) + g αβ δRαβ ,
(2)
βγ
with g αβ δRαβ = ∇α W α , where W α = δΓα
− δΓǫβǫ g βα = g βγ ∇α δΨβγ [6]. When we deal with a manifold M which
βγ g
has a boundary ∂M, the action (1) should be supplemented by a boundary term in order to the variational principle
to be well-defined. This additional term is known as the York-Gibbons-Hawking action[3, 4]. In this letter we shall
propose other solution for this problem. Our strategy will be to preserve the Einstein-Hilbert action as in (1) and see
what are the consequences of do it.
When the flux of W α that across the Gaussian-like hypersurface is nonzero, one obtains in the last term of (2), that
∇α W α = Φ(xα ).
(3)
Here, Φ(xα ) is an arbitrary scalar field which becomes zero when the manifold has no boundary. In order to make
δI = 0 in (2), we shall consider the condition: Gαβ + κTαβ = Λ gαβ , where Λ is the cosmological constant, which
is a relativistic invariant. Additionally, we must require (3), with the constriction δgαβ Λ = Φ gαβ . We propose
the existence of a tensor field δΨαβ , such that δRαβ ≡ ∇β Wα − Φ gαβ ≡ δΨαβ − Φ gαβ = −κ δSαβ 1 , and hence
∗
1
E-mail address: [email protected]
We have introduced the tensor Sαβ = Tαβ − 12 T gαβ , which takes into account matter as a source of the Ricci tensor Rαβ .
Precessional instability in binary black holes with aligned spins
Davide Gerosa,1, ∗ Michael Kesden,2, † Richard O’Shaughnessy,3, ‡ Antoine Klein,4, §
Emanuele Berti,4, 5, 6, ¶ Ulrich Sperhake,1, 4, 5, ∗∗ and Daniele Trifir`o4, 7, ††
1
arXiv:1506.09116v1 [gr-qc] 30 Jun 2015
Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences,
University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK
2
Department of Physics, The University of Texas at Dallas, Richardson, TX 75080, USA
3
Center for Computational Relativity and Gravitation,
Rochester Institute of Technology, Rochester, NY 14623, USA
4
Department of Physics and Astronomy, The University of Mississippi, University, MS 38677, USA
5
California Institute of Technology, Pasadena, CA 91125, USA
6
CENTRA, Departamento de F´ısica, Instituto Superior T´ecnico,
Universidade de Lisboa, Avenida Rovisco Pais 1, 1049 Lisboa, Portugal
7
Dipartimento di Fisica E. Fermi, Universit`
a di Pisa, Pisa 56127, Italy
(Dated: July 1, 2015)
Binary black holes on quasicircular orbits with spins aligned with their orbital angular momentum
have been testbeds for analytic and numerical relativity for decades, not least because symmetry
ensures that such configurations are equilibrium solutions to the spin-precession equations. In this
work, we show that these solutions can be unstable when the spin of the higher-mass black hole
is aligned with the orbital angular momentum and the spin of the lower-mass black hole is antialigned. Spins in these configurations are unstable to precession to large misalignment when the
√
√
binary separation r is between the values rud± = ( χ1 ± qχ2 )4 (1 − q)−2 M , where M is the total
mass, q ≡ m2 /m1 is the mass ratio, and χ1 (χ2 ) is the dimensionless spin of the more (less) massive
black hole. This instability exists for a wide range of spin magnitudes and mass ratios and can occur
in the strong-field regime near merger. We describe the origin and nature of the instability using
recently developed analytical techniques to characterize fully generic spin precession. This instability
provides a channel to circumvent astrophysical spin alignment at large binary separations, allowing
significant spin precession prior to merger affecting both gravitational-wave and electromagnetic
signatures of stellar-mass and supermassive binary black holes.
PACS numbers: 04.25.dg, 04.70.Bw, 04.30.-w
Introduction. – Black holes (BHs) have been observed in two distinct regimes: stellar-mass BHs
(5M . m . 100M ) accrete from companions in X-ray
binaries [1–3], while supermassive BHs shine as quasars
or active galactic nuclei (AGN) [4, 5]. Both types of
BHs naturally occur in binaries: the massive stellar progenitors of stellar-mass BHs are typically formed in binaries, while supermassive BHs form binaries following
the mergers of their host galaxies [6]. Gravitational radiation circularizes the orbits of these binaries [7] and
causes them to inspiral and eventually merge, making
them promising sources of gravitational waves (GWs) for
current and future GW detectors [8–15]. The spins of
these binary BHs need not be aligned with their orbital
angular momentum: stellar-mass BHs may recoil during
asymmetric collapses tilting their spins with respect to
the orbital plane [16–18], while the initial orbital plane
of supermassive BH binaries reflects that of their host
galaxies and is thus independent of their spin. Gravitational effects alone will not align the BH spins with
the orbital angular momentum [19, 20], but astrophysical mechanisms exist that drive the BH spins towards
alignment in both regimes. The first BH to collapse in
stellar-mass BH binaries may accrete in a disk from its
as yet uncollapsed companion, while both members of
a supermassive BH binary may accrete from a common
circumbinary disk. Warps in these accretion disks can
align the BH spins with the orbital angular momentum
[21–23], but if the initial misalignment between the BH
spin and accretion disk is greater than 90◦ , the BH may
instead be driven into anti-alignment [24].
Misaligned spins cause the orbital angular momentum
to precess [25–27], modulating the emitted GWs [28].
Spin misalignment is both a blessing and a curse for GW
data analysis: it increases the parameter space of templates needed to detect GWs via matched filtering but
also breaks degeneracies between estimated parameters
in detected events [29]. Spin misalignment has astrophysical implications: misaligned spins at merger can generate large gravitational recoils [30–32], ejecting supermassive BHs from their host galaxies, and may also explain
the observed “X-shaped” morphology of AGN radio lobes
[33]. Given the importance of spin misalignment, it is
worth investigating the robustness of aligned spin configurations. In the general case that the BHs have unequal
masses, there are four distinct (anti-)aligned configurations, which we refer to as up-up, up-down, down-up, and
down-down. The direction before (after) the hyphen describes the more (less) massive BH and up (down) implies
(anti-)alignment of the spin with the orbital angular momentum. By symmetry, all four configurations are equilibrium solutions to the orbit-averaged spin-precession
arXiv:1506.09057v1 [nucl-th] 30 Jun 2015
European Physical Journal Web of Conferences will be set by the publisher
DOI: will be set by the publisher
c Owned by the authors, published by EDP Sciences, 2015
Symmetry energy systematics and its high density behavior
Lie-Wen Chen1,a
1
Department of Physics and Astronomy and Shanghai Key Laboratory for Particle Physics and Cosmology,
Shanghai Jiao Tong University, Shanghai 200240, China
Abstract. We explore the systematics of the density dependence of nuclear
matter symmetry energy in the ambit of microscopic calculations with various
energy density functionals, and find that the symmetry energy from subsaturation density to supra-saturation density can be well determined by three
characteristic parameters of the symmetry energy at saturation density ρ0 , i.e.,
the magnitude Esym (ρ0 ), the density slope L and the density curvature Ksym .
This finding opens a new window to constrain the supra-saturation density behavior of the symmetry energy from its (sub-)saturation density behavior. In
particular, we obtain L = 46.7 ± 12.8 MeV and Ksym = −166.9 ± 168.3 MeV as
well as Esym (2ρ0 ) ≈ 40.2±12.8 MeV and L(2ρ0 ) ≈ 8.9±108.7 MeV based on the
present knowledge of Esym (ρ0 ) = 32.5 ± 0.5 MeV, Esym (ρc ) = 26.65 ± 0.2 MeV
and L(ρc ) = 46.0 ± 4.5 MeV at ρc = 0.11 fm−3 extracted from nuclear mass and
the neutron skin thickness of Sn isotopes. Our results indicate that the symmetry energy cannot be stiffer than a linear density dependence. In addition,
we also discuss the quark matter symmetry energy since the deconfined quarks
could be the right degree of freedom in dense matter at high baryon densities.
1 Introduction
The nuclear matter symmetry energy, which essentially characterizes the isospin dependent
part of the equation of state (EOS) of asymmetric nuclear matter, is important for understanding many questions in nuclear physics and astrophysics, including the nuclear effective
interactions in asymmetric nuclear matter, the structure and stability of exotic nuclei, the reaction dynamics induced by rare isotopes, the nature and evolution of neutron stars, and the
mechanism of supernova explosion [1–7]. The symmetry energy also plays an important role
in some interesting issues of new physics beyond the standard model [8–12]. During the last
decade, a lot of experimental, observational and theoretical efforts have been devoted to constraining the density dependence of the symmetry energy [13–18]. While significant progress
has been made in determining the density behavior of the symmetry energy around saturation density ρ0 (∼ 0.16 fm−3 ), its supra-saturation density behavior is still poorly known and
remains the most uncertain property of isospin asymmetric nuclear matter. Theoretically,
many experimental and observational probes have been proposed to extract information on
the supra-saturation density behavior of the symmetry energy [13]. In terrestrial laboratories,
a e-mail: [email protected]
Toyama International Workshop on Higgs as a Probe of New Physics 2015, 11–15, February, 2015
XMASS: Recent results and status
K. Hiraide1,2 , for the XMASS Collaboration
1
arXiv:1506.08939v1 [physics.ins-det] 30 Jun 2015
Kamioka Observatory, Institute for Cosmic Ray Research,
the University of Tokyo, Higashi-Mozumi, Kamioka, Hida, Gifu, 506-1205, Japan
2
Kavli Institute for the Physics and Mathematics of the Universe,
the University of Tokyo, Kashiwa, Chiba, 277-8582, Japan
The XMASS project is designed for multiple physics goals using highly-purified liquid xenon
scintillator in an ultra-low radioactivity environment. As the first stage of the project, the detector
with 835 kg of liquid xenon was constructed and is being operated. In this paper, we present results
from our commissioning data, current status of the experiment, and a next step of the project.
I.
INTRODUCTION
The XMASS project is designed to detect dark matter, neutrinoless double beta decay, and 7 Be/pp solar
neutrinos using highly-purified liquid xenon scintillator in an ultra-low radioactivity environment [1]. The
advantages of using liquid xenon are a large amount of scintillation light yield, scalability of the size of the
detector mass, an easy purification to reduce internal radioactive backgrounds, and a high atomic number
(Z = 54) to shield radiations from outside of the detector. As the first stage of the XMASS project (XMASS-I),
the detector with 835 kg of liquid xenon was constructed. Its construction started in April 2007 and completed
in September 2010. After completion of the detector, commissioning data was taken from December 2010 to
May 2012. In order to reduce the backgrounds, detector refurbishment was conducted. After a year of the
detector refurbishment, data-taking resumed in November 2013 and is continuing for more than a year till now.
In this paper, we present physics results from our commissioning data, the detector refurbishment and current
status of the experiment, and a next step of the project.
II.
THE XMASS-I DETECTOR
XMASS-I is a single phase liquid xenon scintillator detector located underground (2700 m water equivalent)
at the Kamioka Observatory. It contains 835 kg of liquid xenon in an active region. The volume is viewed by 630
hexagonal and 12 cylindrical Hamamatsu R10789 photomultiplier tubes (PMTs) arranged on an 80 cm diameter
pentakis-dodecahedron support structure. A total photocathode coverage of more than 62% is achieved. The
spherical arrays of PMTs are arranged in a double wall vessel made of oxygen free high conductivity (OFHC)
copper. The detector is calibrated regularly with a 57 Co source inserted along the central vertical axis of the
detector. By the data taken with the 57 Co source at the center of the detector volume, the photoelectron
yield was determined to be ∼14 photoelectrons/keVee where the subscript ee stands for the electron equivalent
energy deposition. In order to shield the liquid xenon detector from external gammas, neutrons, and muoninduced backgrounds, the copper vessel was placed at the center of a φ10 m× 10.5 m cylindrical tank filled with
pure water. The water tank is equipped with 72 Hamamatsu R3600 20-inch PMTs to provide both an active
muon veto and passive shielding against these backgrounds. XMASS-I is the first direct detection dark matter
experiment equipped with such an active water Cherenkov shield. The liquid xenon and water Cherenkov
detectors are hence called an Inner Detector (ID) and an Outer Detector (OD), respectively. More details are
described in Ref. [2].
III.
RESULTS FROM 6.7 LIVE DAYS OF THE LOW ENERGY THRESHOLD DATA
Owing to the large photoelectron yield we achieved, the XMASS-I detector has an advantage in lowering the
energy threshold. Hence, a part of commissioning data was taken with a low trigger threshold of four PMT hits
which corresponds to 0.3 keVee . Two physics results were obtained using 6.7 live days of data collected with
the lowest energy threshold. In order to achieve optimal sensitivity, the entire detector mass of 835 kg was used
because fiducialization is increasingly difficult at these low energies.
1
arXiv:1506.08918v1 [gr-qc] 30 Jun 2015
Cosmology In Terms Of The Deceleration
Parameter. Part II
Yu.L. Bolotin, V.A. Cherkaskiy, O.A. Lemets
D.A. Yerokhin and L.G. Zazunov
”All of observational cosmology is the search
for two numbers: H0 and q0 .”
Allan Sandage, 1970
Abstract
In the early seventies, Alan Sandage defined cosmology as the search for
two numbers: Hubble parameter H0 and deceleration parameter q0 . The first
of the two basic cosmological parameters (the Hubble parameter) describes
the linear part of the time dependence of the scale factor. Treating the
Universe as a dynamical system it is natural to assume that it is non-linear:
indeed, linearity is nothing more than approximation, while non-linearity
represents the generic case. It is evident that future models of the Universe
must take into account different aspects of its evolution. As soon as the
scale factor is the only dynamical variable, the quantities which determine
its time dependence must be essentially present in all aspects of the Universe’
evolution. Basic characteristics of the cosmological evolution, both static and
dynamical, can be expressed in terms of the parameters H0 and q0 . The very
parameters (and higher time derivatives of the scale factor) enable us to
construct model-independent kinematics of the cosmological expansion.
Time dependence of the scale factor reflects main events in history of
the Universe. Moreover it is the deceleration parameter who dictates the
expansion rate of the Hubble sphere and determines the dynamics of the observable galaxy number variation: depending on the sign of the deceleration
parameter this number either grows (in the case of decelerated expansion),
or we are going to stay absolutely alone in the cosmos (if the expansion is
accelerated).
The intended purpose of the report is reflected in its title — ”Cosmology in terms of the deceleration parameter”. We would like to show that
practically any aspect of the cosmological evolution is tightly bound to the
deceleration parameter.
It is the second part of the report. The first part see here http://arxiv.org/abs/1502.00811
Indirect Detection Constraints on the Model Space of Dark Matter Effective Theories
Linda M. Carpenter,1 Russell Colburn,1 and Jessica Goodman1
1
The Ohio State University, Columbus, OH
Using limits on photon flux from Dwarf Spheroidal galaxies, we place bounds on the parameter
space of models in which Dark Matter annihilates into multiple final state particle pair channels.
We derive constraints on effective operator models with Dark Matter couplings to third generation
fermions and to pairs of Standard Model vector bosons. We present limits in various slices of
model parameter space along with estimations of the region of maximal validity of the effective
operator approach for indirect detection. We visualize our bounds for models with multiple final
state annihilations by projecting parameter space constraints onto triangles, a technique familiar
from collider physics; and we compare our bounds to collider limits on equivalent models.
arXiv:1506.08841v1 [hep-ph] 29 Jun 2015
INTRODUCTION
In this era constraints on Dark Matter models are being synthesized from multiple experiments. There has been
much recent work in collider physics, focusing on Dark Matter (DM) models, which include both UV complete theories
and Effective Field Theory (EFT) scenarios. The same models studied in collider physics imply detectable signatures
from Dark Matter annihilation in space. Due to gauge invariance or other theoretical considerations, many of these
models, both EFTs and simplified models, predict couplings between Dark Matter and multiple species of Standard
Model particles. Thus, Dark Matter may be produced in many correlated final state channels at colliders, and may
have multiple final state annihilation channels in space, which would contribute to total detectable photon or positron
flux for satellite experiments.
In this work we explore the indirect detection bounds from Fermi-LAT dwarf spheroidal galaxies [1] on models
where Dark Matter annihilates into multiple final state channels. These bounds are among the tightest constraints
on DM models. We study several EFT models with dimensions 6 and 7 effective operators. We choose operators
which lead to unsuppressed DM annihilation rates in indirect detection processes, and which are being simultaneously
studied in DM production processes at LHC. The dimension 6 operators we study are those which couple Dark Matter
to third generation fermions pairs. The dimension 7 operators we consider are vector boson portals where there DM
couples to multiple pairs of SM gauge bosons.
The use of effective operators allows a great degree of model independence for Dark Matter studies, while capturing
some of the important kinematic features of Dark Matter processes [2–4]. For some models which are completed by
loops, EFT based calculations have so far provided the best means for study at colliders. The limits of the effective
operator paradigm are becoming more clear for collider analyses. In particular, UV completions of models with low
scale messenger portals are less probe-able by colliders, and models with low scale effective operator cut-offs may
not be sensible at collider energies [5–8]. However, we expect that EFT analyses are reliable at the scale of indirect
detection where the center of mass energy of the annihilation process is the same order as the dark matter particle
mass itself. We expect that the EFT treatment is valid down to much lower scales, perhaps for mediator sectors in
range of 10’s of GeV, as opposed to colliders where mediators of some hundred GeV to just under a TeV may not be
appropriate.
We will visualize the bounds we set in two slices of the total parameter space, the plane of fixed DM annihilation
rate, and the plane of effect operator coefficients where the total annihilation rate varies. For the regions of fixed
annihilation rates, we will use the constraints to produce a 2-D visualization of the bounds on a triangle, a technique
familiar from collider physics [9]. We also compare bounds set with the dwarf limits to those set by collider constraints,
and discuss the validity limits of EFTs for both cases.
The format of this paper is as follows, in Section I we will discuss dwarf constraints on photon flux from dark
matter annihilations. In Section II we will analyze constraints on models with non-interfering final state annihilations
and present triangular visualizations of parameter space. In Section III we will analyze a popular set of vector boson
portal models with interfering final state channels. Section IV presents results along with collider constraints and
discusses EFT validity. Section V concludes.
INDIRECT DETECTION FROM DWARF SPHEROIDAL GALAXIES
Dwarf spheroidal galaxies provide some of the tightest constraints on photon flux originating from dark matter
annihilation as they are believed to contain a substantial dark matter component [10, 11]. This combined with their
low astrophysical background makes them a good laboratory to search for dark matter. As no significant excess in the
Baryon number conservation in Bose-Einstein condensate black holes
Florian K¨
uhnel1, ∗ and Marit Sandstad2, †
1
The Oskar Klein Centre for Cosmoparticle Physics, Department of Physics,
Stockholm University, AlbaNova, 106 91 Stockholm, Sweden
2
Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315 Oslo, Norway
(Dated: Wednesday 1st July, 2015, 12:16am)
arXiv:1506.08823v1 [gr-qc] 29 Jun 2015
Primordial black holes are studied in the Bose-Einstein condensate description of space-time.
The question of baryon-number conservation is investigated with emphasis on possible formation
of bound states of the system’s remaining captured baryons. This leads to distinct predictions for
both the formation time, which for the naively natural assumptions is shown to lie between 10−12 s
to 1012 s after Big Bang, as well as for the remnant’s mass, yielding approximately 3 · 1023 kg in the
same scheme. The consequences for astrophysically formed black holes are also considered.
Introduction — The consideration of black holes as objects with important quantum-mechanical properties has
been obvious since Hawking’s discovery of their semiclassical evaporation [1, 2]. At approximately the same
time, though, the issue of baryon number conservation
in black holes was also considered [3–5]. However, this
road has not been pursued much due to the assumption
that baryon-number conservation should be broken or at
least transcended [4] by the black hole. This and other
related manifestations of the no-hair theorem have not
been understood in any semi-classical approach.
A fully quantum proposal has been made by Dvali and
Gomez to describe black holes, and other space-time geometries, as the results of certain peculiar configurations
of a background Bose-Einstein condensate of gravitons
[6–8] (see [9–20] for recent developments). Therein it is
indeed possible to resolve all semi-classical paradoxes, in
particular the one mentioned before. In this approach,
any other species, like a baryon, which is captured by the
black hole is strongly bound by the self-sustained bound
state of condensed gravitons which make up the black
hole. Now, the very mechanism which is responsible for
Hawking radiation, namely quantum depletion, is also
responsible for emission of any captured quantum, which
is fully released over the life time of the black hole.
It is the aim of this paper to review the issue of baryon
number conservation as well as the formation of related
bound states in this novel corpuscular formulation of
black holes. This shall be done in the context of black
holes created in the very early Universe, i.e. primordial
black holes [21, 22], but we will also consider briefly the
consequences for black holes formed from the astrophysical collapses of very massive stars. Specifically we wish to
consider possible formation of bound states of remaining
baryons as first hypothesised in [3] thereby quantifying
the consequences of the baryon conservation in the BoseEinstein condensate considered in [8].
Primordial black holes — Primordial black holes are
black holes formed in the very early Universe [21, 22].
They are generally assumed to form when a critical mass
over-density crosses the horizon and can subsequently
create a horizon-size black hole. These over-densities can
theoretically stem from the extreme ends of the initial
inflationary spectrum or can also be sourced by exotic
early-Universe phenomena such as cosmic string loops or
bubble collisions (c.f. [23] for a recent review).
As these collapse more or less immediately after crossing the horizon, the initial mass M∗ of the black holes
they form are given as the mass of a black hole with
Schwarzschild radius equal to the horizon size at their
formation time t∗ . This can be found to be roughly of
the order [24]:
c3 t∗
t∗
M∗ ≈
kg ,
(1)
≈ 1012
GN
10−23 s
with c being the speed of light, and GN is Newton’s constant. It is assumed that primordial black holes will
not accrete substantially, so that their evolution is determined more or less only by the Hawking evaporation
process that they undergo. Thus from the evaporation of
the black hole we can define a lifetime tlife given by [2]:
3
M∗
tlife ≈ 1071
s,
(2)
M
where M is the solar mass.1 Since primordial black
holes formed later then t ≈ 10−23 s, i.e. of a mass M >
1013 kg have lifetimes longer than the current age of the
Universe, primordial black holes are potential candidates
for dark matter in the Universe. For most masses the
possible fraction of the dark matter that can be in the
form of primordial black holes are constrained by the nondetection of their expected observable effects (see [23, 25]
for recent reviews).
1
For the extremely low mass black holes, the lifetime is shortened by the possibility of evaporation through additional particle species as the small black holes have higher temperature.
For the black holes near the Planck mass M ≈ 10−5 g, effects of
the uncertainty principle also comes into play, and the lifetime
is only given as an expectation value of the lifetime.
Graphene Sails with Phased Array Optical Drive - Towards More Practical
Interstellar Probes
Louis K. Scheffer
arXiv:1506.09214v1 [astro-ph.IM] 30 Jun 2015
Howard Hughes Medical Institute
(Dated: July 1, 2015)
A spacecraft pushed by radiation has the major advantage that the power source is not included
in the accelerated mass, making it the preferred technique for reaching relativistic speeds. There are
two main technical challenges. First, to get significant acceleration, the sail must be both extremely
light weight and capable of operating at high intensities of the incident beam and the resulting high
temperatures. Second, the transmitter must emit high power beams through huge apertures, many
kilometers in diameter, in order to focus radiation on the sail across the long distances needed to
achieve high final speeds. Existing proposals for the sail use carbon or aluminum films. Aluminum
in particular is limited by a low melting point, and both have low mechanical strength requiring
either a distributed payload or complex rigging. Instead, we propose here a graphene sail, which
offers high absorption per unit weight, high temperature operation, and the mechanical strength
to support simple rigging to a lumped mass payload. For the transmitter, existing proposals use a
compact high power source, and focus the energy with a large (hundreds to thousands of km) spacebased lens. For optical drive proposals in particular, existing proposals require launch from the outer
solar system, have severe pointing restrictions, and require difficult maneuvering of the beam source.
Here instead we propose an active Fresnel lens operating at optical wavelengths, allowing smaller
apertures of less mass, easier pointing with fewer restrictions, and probe launch from the inner solar
system. The technologies for both the sail and the transmitter are already under development for
other reasons. Worked examples, physically smaller and less massive than those suggested so far,
range from a 1kg payload launched to 10% of the speed of light by a transmitter only 25 times the
mass of ISS, to a larger system that can launch a 1000 kg payload to 50% of the speed of light.
INTRODUCTION
A spacecraft pushed by radiation has the major advantage that the power source is not included in the accelerated mass. This makes it one of the very few techniques that might achieve the velocities needed for interstellar probes with human-scale travel times. However,
the technical problems associated with both the sail and
the source are daunting. The sail must be extremely light
weight, yet either absorb or reflect photons well. Since
high intensities are needed to achieve significant acceleration, it must operate at high temperatures. Finally it
should be mechanically strong to simplify connecting it
to the payload.
The transmitter has a very different, but similarly difficult, set of constraints. To focus radiation out to the required distance, it needs to be physically huge while generating coherent radiation across the aperture. It should
be lightweight since it must operate in space and hence
the components must be launched and maneuvered into
position. It should allow a convenient place for launching
probes, and allow transmitting in different directions, to
launch probes to nearby stars and later send the energy
needed for returning the data.
PREVIOUS WORK
A laser-driven aluminum sail was proposed by Forward
in 1984[1]. The power source was a solar-powered laser,
focussed by a 1000 km diameter Fresnel lens located at 15
AU from the sun, and constructed of concentric rings of
thin plastic film. The system performance was limited by
the melting point of the aluminum sail. The type of laser
source was to be decided later as technogy advanced,
and the details of aiming the laser beam and keeping it
focussed on the probe were not addressed.
A lightweight, microwave-driven probe was introduced
as Starwisp[2], with an aluminum mesh driven by microwave radiation. The microwaves were to be generated
by a solar power satellite, and used only incidentally for
accelerating spacecraft. The wavelength was not optimal
for this application and required a truly enormous lens,
much larger than the Earth. Furthermore, the payload
was tiny, only 4 grams, and had to be distributed across
the sail in even smaller units, a technology not yet mastered and difficult even at a conceptual level. Finally,
later analysis, first informal [3] and then formal[4], determined the aluminum mesh would melt under the proposed illumination. Scaling the power density down to
the point the mesh was not melted reduced the available
acceleration dramatically.
All of these issues were addressed by Landis[4]. After
recognizing that practical materials will operate in absorption and not reflection, he advocated a new figure of
merit for potential sail materials. For a sail dominated
by absorption, the thrust is P/c, where P is the power
absorbed. This energy must be lost by radiation, which
grows as T 4 . Therefore the highest achievable acceleration scales as T 4 /m, where T is the operating tempera-
Prepared for submission to JCAP
arXiv:1506.09209v1 [astro-ph.CO] 30 Jun 2015
Non-Gaussian Structure of B-mode
Polarization after Delensing
Toshiya Namikawaa,b and Ryo Nagatac
a Department
of Physics, Stanford University, Stanford, CA 94305, USA
Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
c High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
b Kavli
E-mail: [email protected], [email protected]
Abstract. The B-mode polarization of the cosmic microwave background on large scales
has been considered as a probe of gravitational waves from the cosmic inflation. Ongoing
and future experiments will, however, suffer from contamination due to the B-modes of nonprimordial origins, one of which is the lensing induced B-mode polarization. Subtraction of
the lensing B-modes, usually referred to as delensing, will be required for further improvement of detection sensitivity of the gravitational waves. In such experiments, knowledge of
statistical properties of the B-modes after delensing is indispensable to likelihood analysis
particularly because the lensing B-modes are known to be non-Gaussian. In this paper, we
study non-Gaussian structure of the delensed B-modes on large scales, comparing them with
those of the lensing B-modes. In particular, we investigate the power spectrum correlation
matrix and the probability distribution function (PDF) of the power spectrum amplitude.
Assuming an experiment in which the quadratic delensing is an almost optimal method, we
find that delensing reduces correlations of the lensing B-mode power spectra between different multipoles, and that the PDF of the power spectrum amplitude is well described as a
normal distribution function with a variance larger than that in the case of a Gaussian field.
These features are well captured by an analytic model based on the 4th order Edgeworth
expansion. As a consequence of the non-Gaussianity, the constraint on the tensor-to-scalar
ratio after delensing is degraded within approximately a few percent, which depends on the
multipole range included in the analysis.
Mon. Not. R. Astron. Soc. 000, 000–000 (0000)
Printed 1 July 2015
(MN LATEX style file v2.2)
FUSE, STIS, and Keck spectroscopic analysis of the
UV-bright star vZ 1128 in M3 (NGC 5272)
P.
Chayer,1⋆ W. V. Dixon,1 A. W. Fullerton,1 B. Ooghe-Tabanou,2,3 and I. N. Reid1
1
Space Telescope Science Institute, Baltimore, MD 21218, USA
Normale Sup´
erieure, Laboratoire de Radio-Astronomie, 28 rue Chomond, 75005 Paris, France
3 Current address: Sciences Po–M´
edialab, 84 rue de Grenelle, 75007 Paris, France
arXiv:1506.09196v1 [astro-ph.SR] 30 Jun 2015
2 Ecole
´
1 July 2015
ABSTRACT
We present a spectral analysis of the UV-bright star vZ 1128 in M3 based on observations with the Far Ultraviolet Spectroscopic Explorer (FUSE), the Space Telescope
Imaging Spectrograph (STIS), and the Keck HIRES echelle spectrograph. By fitting
the H i, He i, and He ii lines in the Keck spectrum with non-LTE H-He models, we
obtain Teff = 36,600 K, log g = 3.95, and log N (He)/N (H) = −0.84. The star’s FUSE
and STIS spectra show photospheric absorption from C, N, O, Al, Si, P, S, Fe, and
Ni. No stellar features from elements beyond the iron peak are observed. Both components of the N v λ1240 doublet exhibit P Cygni profiles, indicating a weak stellar
wind, but no other wind features are seen. The star’s photospheric abundances appear
to have changed little since it left the red giant branch (RGB). Its C, N, O, Al, Si,
Fe, and Ni abundances are consistent with published values for the red-giant stars in
M3, and the relative abundances of C, N, and O follow the trends seen on the cluster
RGB. In particular, its low C abundance suggests that the star left the asymptotic
giant branch before the onset of third dredge-up.
Key words: spectroscopy — stars: abundances — stars: individual: NGC 5272 vZ
1128
1
INTRODUCTION
In the color-magnitude diagrams of globular clusters, UVbright stars are those objects bluer than the red giant branch
and brighter than the horizontal branch. They consist of
stars that are evolving to the white dwarf stage, either from
the asymptotic giant branch (AGB) or directly from the extreme horizontal branch (EHB). Their atmospheric parameters and abundances should thus provide important constraints on theories of mixing and mass-loss in AGB stars
and the formation and evolution of white dwarfs. To study
these effects, we have analyzed archival FUSE, HST/STIS,
and Keck HIRES spectra of vZ 1128, the well-known UVbright star in the globular cluster M3 (NGC 5272).
The star was first catalogued by von Zeipel (1908).
It was studied spectroscopically by Strom & Strom (1970),
who found it to be a cluster member of late-O spectral type,
with an effective temperature 31,500 K < Teff < 35,000 K,
a surface gravity 3.9 < log g < 5.2, a stellar mass M > 0.6
M⊙ , and a helium content similar to that of normal Population I stars. The spectrum showed absorption from N,
⋆
E-mail: [email protected]
c 0000 RAS
O, and Si, but its low resolution precluded a detailed abundance analysis. By comparing 11 UV-bright stars in globular clusters with post-HB evolutionary tracks, Strom et al.
(1970) concluded that most evolved from HB stars, while the
three brightest (including vZ 1128) are post-AGB objects.
Garrison & Albert (1986) derived a spectral type of O8p.
The star’s high temperature makes it a perfect target for far-ultraviolet spectroscopy. It was observed with
the International Ultraviolet Observer by de Boer (1985),
who derived a temperature Teff = 30, 000 ± 2000 K, a surface gravity log g = 4.0, and a luminosity log L/L⊙ =
3.10. Buzzoni et al. (1992) pointed out that these parameters place the star on the post-AGB evolutionary tracks of
Sch¨
onberner (1983) and concluded that the star is a bona
fide post-AGB object. Dixon et al. (1994) observed vZ 1128
with the Hopkins Ultraviolet Telescope and derived Teff =
35, 000 ± 1000 K and log g = 4.0 ± 0.25.
Because vZ 1128 (l = 42.5, b = +78.8) lies 10 kpc above
the Galactic plane along a line of sight with virtually no extinction (E(B − V ) = 0.01; Harris 1996, 2010 edition), it is
often used as a probe of interstellar gas in the Galactic halo
(e.g., de Boer & Savage 1984). Both our FUSE (Howk et al.
2003) and STIS (Howk et al. 2006) data were originally ob-
Tachyon inflation in the N –formalism
Nandinii Barbosa-Cendejas,1, 2, a Josue De-Santiago,3, b
Gabriel German,3, c Juan Carlos Hidalgo,3, d and Refugio Rigel Mora-Luna3, e
1
arXiv:1506.09172v1 [astro-ph.CO] 30 Jun 2015
Instituto de Ciencias F´ısicas, Universidad Nacional Aut´
onoma de M´exico,
Apdo. Postal 48-3, 62251 Cuernavaca, Morelos, M´exico,
2
Facultad de Ingenier´ıa El´ectrica, Universidad Michoacana de San Nicol´
as de Hidalgo, Morelia, Michoac´
an, M´exico
3
Instituto de Ciencias F´ısicas, Universidad Nacional Aut´
onoma de M´exico,
Apdo. Postal 48-3, 62251 Cuernavaca, Morelos, M´exico.
(Dated: July 1, 2015)
We study tachyon inflation within the N –formalism, which takes a prescription for the small
Hubble flow slow–roll parameter 1 as a function of the large number of e-folds N . This leads to a
classification of models through their behaviour at large-N . In addition to the perturbative N class,
we introduce the polynomial and exponential classes for the 1 parameter. With this formalism we
reconstruct a large number of potentials used previously in the literature for tachyon field inflation.
We also obtain new families of potentials form the polynomial class. We characterize the realizations
of Tachyon inflation by computing the usual cosmological observables at first and second order in
the Hubble flow slow–roll parameters. This allows us to look at observable differences between
tachyon and canonical scalar field inflation. The analysis of observables in light of the Planck 2015
data shows the viability of some of these models, mostly for certain realization of the polynomial
and exponential classes.
PACS numbers: 11.25.Mj, 04.40.Nr, 11.10.Kk
I.
INTRODUCTION
From its inception, inflation has been a very successful idea to help understand several issues which the old cosmology
was unable to explain [1]. The paradigm of inflation has involved a vast effort in model building and the variety of
models is huge. A favoured type of models is single field inflation where inflation is driven by a single scalar field
field. The nature of the scalar field is not yet determined and in principle the tachyon can be responsible for inflation.
The tachyon field was brought up to prominence by A. Sen [2, 3] who studied type II string theory and the tachyon
instability signals on D-branes, in the context of the brane wold paradigm the tachyon field as also been a subject of
study see for instance [4] and references there in. The cosmological relevance of the tachyon was indicated in [5], where
the expansion of the universe was studied for various initial conditions. More recent references can be found in [6–9].
Independently of its possible origin in string theory one can simply take the tachyon field as another inflaton candidate
and study its implications without trying (for the moment) to understand its origin and theoretical implications.
In the present article we study tachyon inflation in the so called N –formalism [10–12], where relevant quantities are
functions of the number of e-folds N , taken as an evolution variable, instead of the usual inflaton field φ, or cosmic
time. The N –formalism has been successfully applied to obtain model–independent predictions for the scalar spectral
index [13] as well as for the running [12] in the canonical single-field inflation scenario. Interesting results for the
excursion ∆φ of the inflaton have obtained in [14] within this formalism.
In practice, the N –formalism is employed to obtain universal classes of inflationary models from the mathematical
relations that represent two general physical conditions, namely a large number of e-folds and a small slow–roll
parameters. In the N –formalism these two requirements are linked in a single prescription that stipulates a long
period of inflation. Concretely, these two conditions impose a prescription on the Hubble flow slow–roll parameter 1 ,
which also plays the role of an equation of state parameter. An explicit form of 1 (N ) allows one to group families
of potentials in a single prescription with common functional forms for the observables. The N –formalism represents
a powerful method of extracting important information about complete classes of inflationary models in a condensed
way; as opposed to the usual treatment of individual models starting from an explicit potential.
a Electronic
address:
address:
address:
d Electronic address:
e Electronic address:
b Electronic
c Electronic
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
Submitted to the Astronomical Journal
arXiv:1506.09157v1 [astro-ph.EP] 30 Jun 2015
Tidal Evolution of Asteroidal Binaries.
Ruled by Viscosity. Ignorant of Rigidity.
Michael Efroimsky
US Naval Observatory, Washington DC 20392 USA
e-mail: michael.efroimsky @ usno.navy.mil
July 1, 2015
Abstract
This is a pilot paper serving as a launching pad for study of orbital and spin
evolution of binary asteroids. The rate of tidal evolution of asteroidal binaries
is defined by the dynamical Love numbers kl divided by quality factors Q .
Common in the literature is the (oftentimes illegitimate) approximation of the
dynamical Love numbers with their static counterparts. Since the static Love
numbers are, approximately, proportional to the inverse rigidity, this renders a
popular fallacy that the tidal evolution rate is determined by the product of
the rigidity by the quality factor: kl /Q ∝ 1/(µQ) . In reality, the dynamical
Love numbers depend on the tidal frequency and all rheological parameters of
the tidally perturbed body (not just rigidity). We demonstrate that in asteroidal binaries the rigidity of their components plays virtually no role in tidal
friction and tidal lagging, and thereby has almost no influence on the intensity
of tidal interactions (tidal torques, tidal dissipation, tidally induced changes of
the orbit). A key quantity that overwhelmingly determines the tidal evolution
is a product of the effective viscosity η by the tidal frequency χ . The functional form of the torque’s dependence on this product depends on who wins
in the competition between viscosity and self-gravitation. Hence a quantitative
criterion, to distinguish between two regimes. For higher values of ηχ , we get
kl /Q ∝ 1/(ηχ) ; while for lower values we obtain kl /Q ∝ ηχ . Our study rests
on an assumption that asteroids can be treated as Maxwell bodies. Applicable
to rigid rocks at low frequencies, this approximation is used here also for rubble
piles, due to the lack of a better model. In the future, as we learn more about
mechanics of granular mixtures in a weak gravity field, we may have to amend
the tidal theory with other rheological parameters, ones that do not show up in
the description of viscoelastic bodies. This line of study provides a tool to exploring the orbital history of asteroidal pairs, as well as of their final spin states.
1
Astronomy & Astrophysics manuscript no. ERA_3.1.5
c
ESO
2015
July 1, 2015
The ERA Method with Idealizing PSF for Precise
Weak Gravitational Lensing Shear Analysis
arXiv:1506.09156v1 [astro-ph.CO] 30 Jun 2015
Yuki Okura1 and Toshifumi Futamase2
1
RIKEN, [email protected]
2
Tohoku University, [email protected]
July 1, 2015
ABSTRACT
We generalize ERA method of PSF correction for more realistic situations. The method re-smears
the observed galaxy image(galaxy image smeared by PSF) and PSF image by an appropriate
function called Re-Smearing Function(RSF) to make new images which have the same ellipticity
with the lensed (before smeared by PSF) galaxy image. It has been shown that the method avoids
a systematic error arising from an approximation in the usual PSF correction in moment method
such as KSB for simple PSF shape. By adopting an idealized PSF we generalize ERA method
applicable for arbitrary PSF. This is confirmed with simulated complex PSF shapes. We also
consider the effect of pixel noise and found that the effect causes systematic overestimation.
Use \titlerunning to supply a shorter title and/or \authorrunning to supply a shorter list of authors.
1. Introduction
It is now widely recognized that weak gravitational lensing is an unique and powerful tool to obtain mass distribution in the universe. Coherent deformation of the shapes of background galaxies
carries not only the information of intervening mass distribution but also the cosmological background geometry and thus the cosmological parameters(Mellier 1999, Schneider 2006, Munshi et
al. 2008).
In fact weak lensing studies have revealed the averaged mass profile for galaxy cluster (Okabe
et al. 2013, Umetsu et al. 2014) and detected the cosmic shear that is weak lensing by large scale
structure is expected to be useful for studying the property of dark energy. However the signal of
cosmic shear is very weak and difficult to get useful constraint on the dark energy. Currently, several
surveys are just started and planned to measure the cosmic shear accurately enough to constrain the
dark energy property, such as Hyper Suprime-Cam on Subaru (http://www.naoj.org/Projects/HSC/HSCProject.html),
Article number, page 1 of 12
Inflation, evidence and falsifiability
Giulia Gubitosi,1, ∗ Macarena Lagos,1, 2, † Jo˜ao Magueijo,1, ‡ and Rupert Allison2, §
arXiv:1506.09143v1 [astro-ph.CO] 30 Jun 2015
1
Theoretical Physics, Blackett Laboratory, Imperial College, London, SW7 2BZ, UK
2
Astrophysics, University of Oxford, DWB, Keble Road, Oxford OX1 3RH, UK
(Dated: July 1, 2015)
In this paper we consider the issue of paradigm evaluation by applying Bayes’ theorem along the
following nested chain of progressively more complex structures: i) parameter estimation (within a
model), ii) model selection and comparison (within a paradigm), iii) paradigm evaluation. In such a
chain the Bayesian evidence works both as the posterior’s normalization at a given level and as the
likelihood function at the next level up. Whilst raising no objections to the standard application of
the procedure at the two lowest levels, we argue that it should receive an essential modification when
evaluating paradigms, in view of the issue of falsifiability. By considering toy models we illustrate
how unfalsifiable models and paradigms are always favoured by the Bayes factor. We argue that the
evidence for a paradigm should not only be high for a given dataset, but exceptional with respect
to what it would have been, had the data been different. We propose a measure of falsifiability
(which we term predictivity), and a prior to be incorporated into the Bayesian framework, suitably
penalising unfalsifiability. We apply this measure to inflation seen as a whole, and to a scenario
where a specific inflationary model is hypothetically deemed as the only one viable as a result of
information alien to cosmology (e.g. Solar System gravity experiments, or particle physics input).
We conclude that cosmic inflation is currently difficult to falsify and thus to be construed as a
scientific theory, but that this could change were external/additional information to cosmology to
select one of its many models. We also compare this state of affairs to bimetric varying speed of
light cosmology.
I.
INTRODUCTION
As the cosmological data continues to improve with
its inevitable twists, it has become evident that whatever the observations turn out to be they will be lauded
as “proof of inflation”. This was poignantly brought to
the fore when the BICEP2 data was released [1], in the
wake of Planck’s initial cosmological papers [2–5]. Even
though the two datasets taken at face-value contradicted
each other, they were both advertised as proof of inflation. With the demise of the BICEP2 claim no one seems
to have noted the flaw subjacent to this attitude: inflation can in fact predict practically anything. Interesting
sociology will no doubt be reenacted when Planck’s polarisation data makes its mark, in the hopefully not too
distant future.
Independently of where the correct observations end up
settling, matters such as model selection, paradigm evaluation and theoretical prejudice will have to be addressed
before any proper scientific conclusions are drawn. We
should quantify the fact that if inflation seen as a whole
(i.e. as a paradigm) does indeed “fit anything”, then, reciprocally, it cannot be disproved. If we insist on falsifiability as the hallmark of a scientific theory, inflation,
therefore, cannot be scientifically proved, no matter how
well it fits the data. Penalisation schemes for models
which fit the data due to an abundance of free parame-
∗ Electronic
address:
address:
‡ Electronic address:
§ Electronic address:
† Electronic
[email protected]
[email protected]
[email protected]
[email protected]
ters do exist, but transposing these schemes to paradigms
is far from obvious. In this paper we address this problem, hoping to raise at least a modicum of skepticism
regarding the unavoidable successes of a theory which
seemingly can accommodate any observation.
Part of the problem stems from the widespread use of
the concept of Bayesian evidence and the Bayes factor.
As explained in Section II, Bayes’ theorem may be used
in nested chains involving qualitatively very different levels, such as parameter estimation (within a given model),
model selection (within a paradigm), and paradigm evaluation. The Bayes factor is usually employed to compare models or for finding the best-fit parameters for a
specific model, for which the concept is perfectly adequate because the various options under comparison are
roughly equally predictive. The limitations of the existing formalism emerge, however, as soon as we insist on
falsifiability as a pre-requisite for a scientific theory.
We note that the Bayesian evidence does penalise
“spreading the bets” or employing too many parameters,
but not sufficiently harshly when the issue of falsifiability
is relevant. In fact, the concept is more suited to playing the lottery than to enforcing falsifiability: winning
is more important than being predictive. Thus, missing the jackpot is penalised exponentially by the Bayes
factor, whereas being unpredictive is only penalised as
a power-law. A modification of the concept is required
if we insist on science being not about playing the lottery and winning, but about falsifiability, that is, about
winning given that you have taken the full brunt of the
risk of losing. We illustrate this issue in Section III by
means of a number of toy models, some grotesquely predictive/unpredictive, others less black and white.
A new halo model for clusters of galaxies
Erhard Scholz∗
arXiv:1506.09138v1 [astro-ph.CO] 30 Jun 2015
June 30, 2015
Abstract
This paper presents a model for the dark halos of galaxy clusters in
the framework of Weyl geometric scalar tensor theory with a MONDlike approximation in the weak field static limit. The basics of this
approach are introduced in the first part of the paper; then a three
component halo model is derived (without presupposing prior knowledge of Weyl geometric gravity). The cluster halo is constituted by the
scalar field energy and the phantom energy of the gravitational structure, thus transparent rather than “dark”. It is completely determined
by the baryonic mass distribution of hot gas and stars. The model is
tested against recent observational data for 19 clusters [13], [14]. The
total mass of Coma and 15 other clusters is correctly predicted on the
basis of data on baryonic mass in the bounds of the error intervals
(1 σ); one cluster lies in the 2 σ interval, two more in 3 σ.
Contents
Introduction
2
1 Theoretical framework
1.1 Weyl geometric scalar tensor theory of gravity (W-ST) . . .
1.2 The weak field static approximation . . . . . . . . . . . . .
1.3 W-ST gravity with cubic kinematic Lagrangian (W-ST-3L)
1.4 A new relativistic approach to MOND . . . . . . . . . . . .
1.5 Short resumé . . . . . . . . . . . . . . . . . . . . . . . . . .
2
Halo model for clusters of galaxies
2.1 Cluster models for baryonic mass (hot gas and stars)
2.2 Scalar field halo and phantom halo of baryonic mass .
2.3 Scalar field halo of galaxy ensemble . . . . . . . . . .
2.4 A three-component halo model for clusters of galaxies
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University of Wuppertal, Department C, Mathematics, and Interdisciplinary Centre
for History and Philosophy of Science; [email protected]
1
Mon. Not. R. Astron. Soc. 000, 1–13 (2015)
Printed 1 July 2015
(MN LATEX style file v2.2)
A simplified view of blazars: the neutrino background
P.
Padovani1,2? , M. Petropoulou3 †, P. Giommi4,5 , E. Resconi6
1
European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei M¨
unchen, Germany
to INAF - Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio Catone, Italy
3 Department of Physics and Astronomy, Purdue University, 525 Northwestern Avenue, West Lafayette, IN 47907, USA
4 ASI Science Data Center, via del Politecnico s.n.c., I-00133 Roma Italy
5 ICRANet-Rio, CBPF, Rua Dr. Xavier Sigaud 150, 22290-180 Rio de Janeiro, Brazil
6 Technische Universit¨
at M¨
unchen, Physik-Department, James-Frank-Str. 1, D-85748 Garching bei M¨
unchen, Germany
2 Associated
arXiv:1506.09135v1 [astro-ph.HE] 30 Jun 2015
Accepted ... Received ...; in original form ...
ABSTRACT
Blazars have been suggested as possible neutrino sources long before the recent IceCube discovery of high-energy neutrinos. We re-examine this possibility within a new framework built upon the blazar simplified view and a selfconsistent modelling of neutrino emission from individual sources. The former
is a recently proposed paradigm that explains the diverse statistical properties
of blazars adopting minimal assumptions on blazars’ physical and geometrical
properties. This view, tested through detailed Monte Carlo simulations, reproduces the main features of radio, X-ray, and γ-ray blazar surveys and also the
extragalactic γ-ray background at energies & 10 GeV. Here we add a hadronic
component for neutrino production and estimate the neutrino emission from BL
Lacs as a class, “calibrated” by fitting the spectral energy distributions of a preselected sample of BL Lac objects and their (putative) neutrino spectra. Unlike
all previous papers on this topic, the neutrino background is then derived by
summing up at a given energy the fluxes of each BL Lac in the simulation, all
characterised by their own redshift, synchrotron peak energy, γ-ray flux, etc.
Our main result is that BL Lacs as a class can explain the neutrino background
seen by IceCube above ∼ 0.5 PeV while they only contribute ∼ 10% at lower
energies, leaving room to some other population(s)/physical mechanism. However, one cannot also exclude the possibility that individual BL Lacs still make a
contribution at the ≈ 20% level to the IceCube low-energy events. Our scenario
makes specific predictions testable in the next few years.
Key words: neutrinos — radiation mechanisms: non-thermal — BL Lacertae
objects: general — gamma-rays: galaxies
1
INTRODUCTION
Blazars are a class of Active Galactic Nuclei (AGN),
which host a jet oriented at a small angle with respect
to the line of sight. Highly relativistic particles moving
within the jet and in a magnetic field emit non-thermal
radiation (Blandford & Rees 1978; Urry & Padovani
1995). This is at variance with most other AGN whose
energy is mainly thermal and produced through accretion
of matter onto a supermassive black hole. Because of their
peculiar orientation and highly relativistic state, blazars
are characterised by distinctive and extreme observational properties, including superluminal motion, large
?
E-mail: [email protected]
† Einstein Postdoctoral Fellow
c 2015 RAS
and rapid variability, and strong emission over the entire electromagnetic spectrum. The two main blazar subclasses, namely BL Lacertae objects (BL Lacs) and flatspectrum radio quasars (FSRQ), differ mostly in their
optical spectra, with the latter displaying strong, broad
emission lines and the former instead being characterised
by optical spectra showing at most weak emission lines,
sometimes exhibiting absorption features, and in many
cases being completely featureless.
The spectral energy distributions (SEDs) of blazars
are composed of two broad humps, a low-energy and
a high-energy one. The peak of the low-energy hump
S
(νpeak
) can occur at widely different frequencies, ranging
from about ∼ 1012.5 Hz (∼ 0.01 eV) to ∼ 1018.5 Hz (∼ 13
keV). The high-energy hump, which may extend up to ∼
10 TeV, has a peak energy that ranges between ∼ 1020 Hz
Measurement of the cosmic-ray energy spectrum above 1016 eV with the LOFAR Radboud
Air Shower Array
S. Thoudama,∗, S. Buitinkb , A. Corstanjea , J. E. Enriqueza, H. Falckea,c,d, J. R. H¨orandela,d, A. Nellesa,e , J. P. Rachena , L.
Rossettoa , P. Schellarta , O. Scholtenf,g , S. ter Veena , T. N. G. Trinhf , L. van Kessela
arXiv:1506.09134v1 [astro-ph.IM] 30 Jun 2015
a Department
of Astrophysics, IMAPP, Radboud University Nijmegen, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands
b Astrophysical Institute, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
c ASTRON, 7990 AA Dwingeloo, The Netherlands
d Nikhef, Science Park Amsterdam, 1098 XG Amsterdam, The Netherlands
e Now at: Department of Physics and Astronomy, University of California Irvine, Irvine, CA 92697-4575, USA
f KVI-CART, University of Groningen, 9747 AA Groningen, The Netherlands
g Interuniversity Institute for High-Energy, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
Abstract
The energy reconstruction of extensive air showers measured with the LOFAR Radboud Air Shower Array (LORA) is presented in
detail. LORA is a particle detector array located in the center of the LOFAR radio telescope in the Netherlands. The aim of this
work is to provide an accurate and independent energy measurement for the air showers measured through their radio signal with
the LOFAR antennas. The energy reconstruction is performed using a parameterized relation between the measured shower size
and the cosmic-ray energy obtained from air shower simulations. In order to illustrate the capabilities of LORA, the all-particle
cosmic-ray energy spectrum has been reconstructed, assuming that cosmic rays are composed only of protons or iron nuclei in
the energy range between ∼ 2 × 1016 and 2 × 1018 eV. The results are compatible with literature values and a changing mass
composition in the transition region from a galactic to an extragalactic origin of cosmic rays.
Keywords: Cosmic rays, Air showers, Energy spectrum, LORA
1. Introduction
The quest for the origin of cosmic rays is one of the most fundamental problems in Astroparticle Physics [1, 2, 3]. Since the
discovery of these highly energetic particles more than a century ago, numerous measurements of several of their properties
have been made, using sophisticated instruments (see e.g. Ref.
[4] for a review). However, the exact nature of their sources still
remains an open question. The search is mainly hindered due to
the fact that cosmic rays, being charged particles, are scattered
or deflected by the Galactic and inter-galactic magnetic fields
during their propagation to the Earth, making it extremely difficult to reconstruct the direction of their sources. Nevertheless,
observed cosmic-ray properties like the energy spectrum and
composition have been used to understand and characterize the
properties of the sources such as their Galactic or extragalactic
nature, the cosmic-ray production spectrum and the power injected into cosmic rays (see e.g. Refs. [5, 6, 7, 8, 9, 10, 11] for
recent reviews).
LOFAR, the LOw Frequency ARray, is an astronomical radio
telescope [12]. It has been designed to measure the properties of
cosmic rays above ∼ 1016 eV by detecting radio emission from
extensive air showers in the frequency range of 10 − 240 MHz
[13]. One of the main goals of the LOFAR key science project
∗ Corresponding
author
Email address: [email protected] (S. Thoudam)
Preprint submitted to Astroparticle Physics
Cosmic Rays is to provide an accurate measurement of the mass
composition of cosmic rays in the energy range between ∼ 1016
and ∼ 1018 eV, a region where the transition from Galactic to
extragalactic cosmic rays is expected. This is being carried out
by measuring the depth of the shower maximum (Xmax ), using
a technique based on the reconstruction of the two-dimensional
radio intensity profile on the ground [14, 15]. Another focus
of the LOFAR cosmic-ray measurements is to understand the
nature and production mechanisms of the radio emission from
air showers. This is done by measuring various properties of the
radio signals in great detail such as their polarization properties,
the radio wave front and relativistic time compression effects on
the emission profile [16, 17, 18].
In order to assist the radio measurement of air showers with
LOFAR, we have built a particle detector array LORA (LOFAR
Radboud Air Shower Array) in the center of LOFAR [19]. Its
main objectives are to trigger the read-out of the LOFAR radio antennas to register radio signals from air showers, and to
provide basic air shower parameters such as the position of the
shower axis as well as the energy and the arrival direction of
the incoming cosmic-ray. These parameters are used to crosscheck the reconstruction of air shower properties, based on the
measured radio signals. Currently, given the lack of an absolute
calibration of the radio signals, the cosmic-ray energy is estimated through the reconstruction of the particle data. Therefore, an accurate energy reconstruction with LORA is essential
July 1, 2015
Astronomy & Astrophysics manuscript no. grid
July 1, 2015
c
ESO
2015
Low-metallicity massive single stars with rotation
Evolutionary models applicable to I Zwicky 18
Dorottya Szécsi1 , Norbert Langer1 , Sung-Chul Yoon2 , Debashis Sanyal1 , Selma de Mink3 , Christopher J. Evans4 , and
Tyl Dermine1
1
2
3
arXiv:1506.09132v1 [astro-ph.SR] 30 Jun 2015
4
Argelander-Institut für Astronomie der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
Department of Physics & Astronomy, Seoul National University, Gwanak-ro 1, Gwanak-gu, 151-742, Seoul, South Korea
Astronomical Institute Anton Pannekoek, University of Amsterdam, 1098 XH Amsterdam, The Netherlands
UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
Received July 1, 2015/ Accepted ...
ABSTRACT
Context. Low-metallicity environments such as the early Universe and compact star-forming dwarf galaxies contain many massive
stars. These stars influence their surroundings through intense UV radiation, strong winds and explosive deaths. A good understanding
of low-metallicity environments requires a detailed theoretical comprehension of the evolution of their massive stars.
Aims. We aim to investigate the role of metallicity and rotation in shaping the evolutionary paths of massive stars and to provide
theoretical predictions that can be tested by observations of metal-poor environments.
Methods. Massive rotating single stars with an initial metal composition appropriate for the dwarf galaxy I Zw 18 ([Fe/H]=−1.7) are
modelled during hydrogen burning for initial masses of 9-300 M and rotational velocities of 0-900 km s−1 . Internal mixing processes
in these models were calibrated based on an observed sample of OB-type stars in the Magellanic Clouds.
Results. Even moderately fast rotators, which may be abundant at this metallicity, are found to undergo efficient mixing induced by
rotation resulting in quasi chemically-homogeneous evolution. These homogeneously-evolving models reach effective temperatures
of up to 90 kK during core hydrogen burning. This, together with their moderate mass-loss rates, make them Transparent Wind
Ultraviolet INtense stars (TWUIN star), and their expected numbers might explain the observed He II ionizing photon flux in I Zw 18
and other low-metallicity He II galaxies. Our slowly rotating stars above ∼80 M evolve into late B- to M-type supergiants during
core hydrogen burning, with visual magnitudes up to 19m at the distance of I Zw 18. Both types of stars, TWUIN stars and luminous
late-type supergiants, are only predicted at low metallicity.
Conclusions. Massive star evolution at low metallicity is shown to differ qualitatively from that in metal-rich environments. Our
grid can be used to interpret observations of local star-forming dwarf galaxies and high-redshift galaxies, as well as the metal-poor
components of our Milky Way and its globular clusters.
Key words. stars: low-metallicity – stars: massive – stars: evolution – stars: rotation – stars: main-sequence – stars: red supergiants
1. Introduction
Many of the first stars in the Universe are thought to have
started out very massive and almost metal-free (Abel et al. 2002;
Bromm & Larson 2004; Frebel et al. 2005). Direct observations
of these stars are not possible with current telescopes. However,
low-metallicity massive stars can also be found in the local Universe: some of the nearby dwarf galaxies form massive stars at a
high rate (Tolstoy et al. 2009; Weisz et al. 2014). As these galaxies can be directly observed and as their metallicity happens to
be close to that of the first stars, they can be used as laboratories to study massive stellar evolution at low (i.e. substantially
subsolar) metallicity. Such studies may lead us to a better understanding of the metallicity dependence of stellar evolution,
including the first stars in the Universe.
Apart from the cosmological implications of stars at high
redshift, there are another reasons to study stellar evolution at
low metallicity. The initial chemical composition of a star influences the whole evolutionary path, internal structure, circumstellar surroundings and even the final fate of the star (Meynet &
Maeder 2002; Hirschi et al. 2005; Meynet & Maeder 2005; Brott
et al. 2011; Yoon et al. 2012; Yusof et al. 2013). There is ob-
servational evidence that long-duration gamma-ray bursts tend
to prefer low-metallicity environments (Levesque et al. 2010;
Modjaz et al. 2011; Graham & Fruchter 2013) and high redshifts
(Horváth et al. 2014). Theoretical studies have shown that fast
rotating stars at low metallicity may evolve quasi chemicallyhomogeneously (Yoon et al. 2006; Brott et al. 2011). These
homogeneously-evolving stellar models are predicted to become fast rotating Wolf–Rayet (WR) type objects during the
post main-sequence phase. They are, therefore, candidates of
long-duration gamma-ray burst progenitors within the collapsar
scenario (MacFadyen & Woosley 1999; Yoon & Langer 2005;
Woosley & Heger 2006). Moreover, broad line type Ic supernovae (Arcavi et al. 2010; Sanders et al. 2012) that are associated with gamma-ray bursts (Modjaz et al. 2011; Graham &
Fruchter 2013) as well as the recently identified superluminous
supernovae (Quimby et al. 2011; Lunnan et al. 2013) occur preferentially in low-metallicity dwarf galaxies. This may corroborate the idea that reduced wind mass-loss at low metallicity (Vink
et al. 2001; Mokiem et al. 2007) may allow for rapid rotation
rates (Yoon et al. 2006; Georgy et al. 2009) and very massive
(Langer et al. 2007; Yusof et al. 2013; Kozyreva et al. 2014)
supernova progenitors. A good understanding of the evolution
Article number, page 1 of 34
The Pulsating Pulsar Magnetosphere
arXiv:1506.09130v1 [astro-ph.HE] 30 Jun 2015
K.H. Tsui
Instituto de F´ısica - Universidade Federal Fluminense
Campus da Praia Vermelha, Av. General Milton Tavares de Souza s/n
Gragoat´a, 24.210-346, Niter´oi, Rio de Janeiro, Brasil.
[email protected]
ABSTRACT
Following the basic principles of a charge separated pulsar magnetosphere
(Goldreich & Julian 1969), we consider the magnetosphere be stationary in space,
instead of corotating, and the electric field be uploaded from the potential distribution on the pulsar surface, set up by the unipolar induction. Consequently, the
plasma of the magnetosphere undergoes guiding center drifts of the gyro motion
due to the transverse forces to the magnetic field. These forces are the electric
force, magnetic gradient force, and field line curvature force. Since these plasma
velocities are of drift nature, there is no need to introduce an emf along the field
~ ·B
~ = 0 plasma condition. Furthermore,
lines, which would contradict the Ek = E
there is also no need to introduce the critical field line separating the electron
and ion open field lines. We present a self-consistent description where the magnetosphere is described in terms of electric and magnetic fields and also in terms
of plasma velocities. The fields and velocities are then connected through the
space charge densities self-consistently. We solve the pulsar equation analytically
for the fields and construct the standard steady state pulsar magnetosphere. By
considering the unipolar induction inside the pulsar and the magnetosphere outside the pulsar as one coupled system, and under the condition that the unipolar
pumping rate exceeds the Poynting flux in the open field lines, plasma pressure
can build up in the magnetosphere, in particular in the closed region. This could
cause a periodic openning up of the closed region, leading to a pulsating magnetosphere, which could be an alternative for pulsar beacons. The closed region can
also be openned periodically by the build-up of toroidal magnetic field through
a positive feedback cycle.
Subject headings: (stars:) pulsars : general
Studying the precision of ray tracing techniques with Szekeres models
S. M. Koksbang1, ∗ and S. Hannestad1
arXiv:1506.09127v1 [astro-ph.CO] 30 Jun 2015
1
Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
The simplest standard ray tracing scheme employing the Born and Limber approximations and
neglecting lens-lens coupling is used for computing the convergence along individual rays in mock
N-body data based on Szekeres swiss cheese and onion models. The results are compared with the
exact convergence computed using the exact Szekeres metric combined with the Sachs formalism.
A comparison is also made with an extension of the simple ray tracing scheme which includes
the Doppler convergence. The exact convergence is reproduced very precisely as the sum of the
gravitational and Doppler convergences along rays in LTB swiss cheese and single void models.
This is not the case when the swiss cheese models are based on non-symmetric Szekeres models.
For such models, there is a significant deviation between the exact and ray traced paths and hence
also the corresponding convergences. There is also a clear deviation between the exact and ray
tracing results obtained when studying both non-symmetric and spherically symmetric Szekeres
onion models.
PACS numbers: 98.80.-k, 98.80.Jk, 98.80.Es
I.
INTRODUCTION
With the possible near-future exception of observations based on gravitational waves, all astrophysical
observations are based on light. This makes understanding light propagation a crucial element of both
theoretical and observational cosmology. The light that
is observed in astrophysical observations has propagated
through vast regions of the Universe to reach us. During
its propagation, the light feels the exact, local spacetime
and not some ”average” spacetime described by an
FLRW (Friedmann-Lemaitre-Robertson-Walker) model.
What effects the local inhomogeneities of spacetime
have on light propagation and how important these
effects are, is still up for debate. For redshift-distance
relations it has however been shown that averaging over
many light rays will reduce observations to what one
would see if the light had simply traveled through the
averaged universe model (see e.g. [1–9]). For models
with vanishing backreaction this implies that averaging
over many light rays will yield results corresponding to
FLRW results (for effects of non-vanishing backreaction
on light propagation, see e.g. [9]. See e.g. [10–13] for
introductions and reviews on cosmic backreaction). The
number of geodesics needed to obtain such results can be
quite large though. In addition, some observables, such
as reduced shear and CMB temperature fluctuations,
are not suitable for the needed averaging. It is thus
important to study the effects of inhomogeneities on
light propagation so that the gained knowledge can
be used when interpreting especially high precision
observations.
Much work has gone into using perturbation theory to
study the effects of inhomogeneities on redshift-distance
∗
[email protected]
relations (see e.g. [14–20] for some recent examples).
Another approach is to use exact, inhomogeneous
solutions to Einstein’s equations. Among the most
realistic, exact solutions to Einstein’s equations which
contain dynamical structures are the quasi-spherical
Szekeres models [21] including their spherically symmetric limit, the Lemaitre-Tolman-Bondi (LTB) models
[22–24]. Light propagation through these models has
been vastly studied, especially with the purpose of
studying the effects of inhomogeneities on CMB and
supernova observations (see e.g. [7–9, 25–57] for some
examples) 1 . With the exception of onion models (see
e.g. [38]), these models are double or triple structure
models (see e.g. [60]) and are thus not individually
useful for realistic studies of light propagation over
large distances. A possible method for overcoming
this issue is to combine few-structure models to build
multiple-structure swiss cheese models (first introduced
in [61]). These models have a high degree of complexity
and are thus very important and useful. However, they
suffer from simplicities such as a lack of interaction
between individual structures (”holes”) and often the
holes in the cheese are made up of only a few specific
inhomogeneous models representing structure formation
on a limited scale interval. Perhaps because swiss cheese
models have these insufficiencies, universe models based
on the output from Newtonian N-body simulations are
by many considered the most realistic models of the
real universe - despite their lack of relativistic effects
such as cosmic backreaction [62, 63]. The standard
cosmological setting for studying light propagation
1
Other models breaking either the assumption of homogeneity or
isotropy have also been used to study light propagation. Examples are [58, 59] concerning light propagation in Bianchi and
Stephani models respectively. In this work, the focus will be on
the Szekeres models, as the Szekeres structures are more comparable to structures in typical N-body simulations.
Scalar – Tensor gravity with scalar – matter direct coupling and
its cosmological probe
Jik Su Kim
Pyongyang Astronomical Observatory, Academy of Sciences, Pyongyang, DPR Korea
Chol Jun Kim, Sin Chol Hwang, Yong Hae Ko,
Department of Physics, Kim Il Sung University, Pyongyang, DPR Korea
Abstract
SNIa and CMB datasets have shown both of evolving Newton’s “constant” and a signature of the
coupling of scalar field to matter. These observations motivate the consideration of the scalar-matter
coupling in Jordan frame in the framework of scalar-tensor gravity. So far, majority of the works on
the coupling of scalar to matter has been performed in Einstein frame in the framework of minimally
coupled scalar fields. In this paper, we generalize the original scalar-tensor theories of gravity by
introducing a direct coupling of scalar to matter in the Jordan frame. The combined consideration of
both evolving Newton’s constant and scalar-matter coupling using the recent observation datasets,
shows features different from the previous works. The analysis shows a vivid signature of the scalarmatter coupling. The variation rate of the Newton’s constant is obtained rather greater than that
determined in the previous works.
I. INTRODUCTION
Cosmological observation datasets are opening a wide possibility of test of the various
cosmological models. Nesseris and Perivolaropoulos[1] have shown that Gold dataset of SNIa
yielded some evidence of the scalar–tensor property of gravitation. Making use of Gold
dataset of SNIa[2], they have found the Newton’s gravitation constant to be evolved.
On the other hand, Majerotto, Sapone and Amendola[3] and Guo, Ohta and Tsujikawa [4]
have found that combined analysis of SNLS, CMB, and BAO datasets showed a signature of
direct scalar–matter coupling. The latter, however, had been based on the background of
Einstein tensor gravity.
The above both analyses are making use of almost the same observation datasets, but their
results are quite contradictory, so we cannot be sure which of these models should be
accepted.
As is well known, when the coupling of scalar to background space-time vanishes the
gravity returns to Einstein tensor gravity. Therefore, if we want to elucidate whether both of
scalar–background space–time and scalar–matter couplings do exist or not, one should
construct a more inclusive model than the previous ones[1, 3, 4].
1
Resonant Absorption of Transverse Oscillations and Associated
Heating in a Solar Prominence. II- Numerical aspects
arXiv:1506.09108v1 [astro-ph.SR] 30 Jun 2015
P. Antolin1 , T. J. Okamoto2,8 , B. De Pontieu3,4 , H. Uitenbroek5 , T. Van Doorsselaere6 , T.
Yokoyama7
1
National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588, Japan
2
ISAS/JAXA, Sagamihara, Kanagawa 252-5210, Japan
3
Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Palo Alto, CA
94304, USA
4
Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315
Oslo, Norway
5
National Solar Observatory, PO Box 62, sunspot, NM 88349, USA
6
Centre for Mathematical Plasma Astrophysics, Mathematics Department, KU Leuven,
Celestijnenlaan 200B bus 2400, B-3001 Leuven, Belgium
7
The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
8
Current address: STEL, Nagoya University, Aichi 464-8601, Japan
[email protected]
ABSTRACT
Transverse magnetohydrodynamic (MHD) waves are ubiquitous in the solar
atmosphere and may be responsible for generating the Sun’s million-degree outer
atmosphere. However, direct evidence of the dissipation process and heating from
these waves remains elusive. Through advanced numerical simulations combined
with appropriate forward modeling of a prominence flux tube, we provide the observational signatures of transverse MHD waves in prominence plasmas. We show
that these signatures are characterized by thread-like substructure, strong transverse dynamical coherence, an out-of-phase difference between plane-of-the-sky
motions and LOS velocities, and enhanced line broadening and heating around
most of the flux tube. A complex combination between resonant absorption and
Kelvin-Helmholtz instabilities (KHI) takes place in which the KHI extracts the
energy from the resonant layer and dissipates it through vortices and current
sheets, which rapidly degenerate into turbulence. An inward enlargement of the
boundary is produced in which the turbulent flows conserve the characteristic
dynamics from the resonance, therefore guaranteeing detectability of the resonance imprints. We show that the features described in the accompanying paper
(Okamoto et al. 2015) through coordinated Hinode and IRIS observations match
well the numerical results.
Solar Physics
DOI: 10.1007/•••••-•••-•••-••••-•
Quiescent and Eruptive Prominences at Solar
Minimum: A Statistical Study via an Automated
Tracking System
I.P. Loboda1 · S.A. Bogachev1
arXiv:1506.09102v1 [astro-ph.SR] 30 Jun 2015
© Springer ••••
Abstract
We employ an automated detection algorithm to perform a global study of solar
prominence characteristics. We process four months of TESIS observations in
the He ii 304 ˚
A line taken close to the solar minimum of 2008–2009 and focus
mainly on quiescent and quiescent-eruptive prominences. We detect a total of
389 individual features ranging from 25 × 25 to 150 × 500 Mm2 in size and obtain
distributions of many their spatial characteristics, such as latitudinal position,
height, size and shape. To study their dynamics, we classify prominences as
either stable or eruptive and calculate their average centroid velocities, which
are found to be rarely exceeding 3 km s−1 . Besides, we give rough estimates
of mass and gravitational energy for every detected prominence and use these
values to evaluate the total mass and gravitational energy of all simultaneously
existing prominences (1012 –1014 kg and 1029 –1031 erg, respectively). Finally, we
investigate the form of the gravitational energy spectrum of prominences and
derive it to be a power-law of index −1.1 ± 0.2.
Keywords: Prominences, Quiescent; Prominences, Dynamics; Prominences,
Formation and Evolution
1. Introduction
Prominences are one of the most noticeable features of the Sun, which, although
observed for over a century, are still far from being completely understood.
For historical reasons, a distinction is made between prominences, observed
off-limb as luminous formations, and filaments, usually seen in absorption on
the disk. Physically, these are the same structures consisting of plasma with
properties similar to those of the chromosphere being nearly 100 times denser
and cooler than the surrounding corona (Hirayama, 1985; Tandberg-Hanssen,
1 P.N. Lebedev Physical Institute of the Russian Academy of
Sciences, Moscow, Russia
email: [email protected]
SOLA: promstat.tex; 1 July 2015; 0:29; p. 1
arXiv:1506.09072v1 [astro-ph.EP] 30 Jun 2015
No evidence for activity correlations in the radial velocities of
Kapteyn’s star
G. Anglada-Escud´e1,2 , M. Tuomi 1 , P. Arriagada3 , M. Zechmeister2 , J. S. Jenkins4 , A.
Ofir5 , S. Dreizler6 , E. Gerlach7 , C. J. Marvin6 , A. Reiners6 , S. V. Jeffers6 , R. Paul Butler3 ,
S. S. Vogt8 , P. J. Amado9 , C. Rodr´ıguez-L´opez9 , Z. M. Berdi˜
nas9 , J. Morin10 , J. D.
Crane11 , S. A. Shectman11 , M. D´ıaz4 , L. F. Sarmiento6 , H. R. A. Jones1
ABSTRACT
Stellar activity may induce Doppler variability at the level of a few m/s which can then be
confused by the Doppler signal of an exoplanet orbiting the star. To first order, linear correlations
between radial velocity measurements and activity indices have been proposed to account for any
such correlation. The likely presence of two super-Earths orbiting Kapteyn’s star was reported in
Anglada-Escud´e et al. (2014), but this claim was recently challenged by Robertson et al. (2015b)
arguing evidence of a rotation period (143 days) at three times the orbital period of one of the
proposed planets (Kapteyn’s b, P=48.6 days), and the existence of strong linear correlations
between its Doppler signal and activity data. By re-analyzing the data using global optimization
methods and model comparison, we show that such claim is incorrect given that; 1) the choice
of a rotation period at 143 days is unjustified, and 2) the presence of linear correlations is not
supported by the data. We conclude that the radial velocity signals of Kapteyn’s star remain more
simply explained by the presence of two super-Earth candidates orbiting it. We also advocate
for the use of global optimization procedures and objective arguments, instead of claims lacking
of a minimal statistical support.
Subject headings: techniques: radial velocities – stars: individual: Kapteyn’s star, planetary systems
1.
Introduction
1
Centre for Astrophysics Research, University of Hertfordshire, College Lane, AL10 9AB, Hatfield, UK
2 School of Physics and Astronomy, Queen Mary, University of London, 327 Mile End Rd. London, United Kingdom
3 Carnegie Institution of Washington, Dept. of Terrestrial Magnetism, 5241 Broad Branch Rd. NW, 20015,
Washington D.C., USA
4 Departamento de Astronom´
ıa, Universidad de Chile,
Camino El Observatorio 1515, Las Condes, Santiago, Chile,
Casilla 36-D.
5 Department of Earth and Planetary Sciences, Weizmann Institute of Science, 234 Herzl St., Rehovot 76100,
Israel
6 Universit¨
at G¨
ottingen, Institut f¨
ur Astrophysik,
Friedrich-Hund-Platz 1, 37077 G¨
ottingen, Germany
7 Institut f¨
ur Planetare Geod¨
asie Technische Universit¨
at
Dresden 01062, Dresden, Germany
8 UCO/Lick Observatory, University of California,
Santa Cruz, CA, 95064, USA
9 Instituto de Astrof´
ısica de Andaluc´ıa-CSIC, Glorieta
Recently, the search for low-amplitude signals in radial velocity time-series has reached
the point where detection of Doppler signals at
the level of 1m/s or less is technically possible (Pepe et al. 2011; Tuomi & Anglada-Escud´e
2013). Along with this rise in precision have
come claims, and counter-claims, of the detection of planetary systems containing very lowmass planets (e.g. α Centauri, Dumusque et al.
2012, Hatzes 2013; HD 41248 Jenkins et al.
2013; Jenkins & Tuomi 2014, Santos et al. 2014;
de la astronom´ıa S/N, 18008, Granada, Spain
10 LUPM-UMR5299, CNRS & Universitde
´ Montpellier,
Place E. Bataillon, Montpellier, F-34095, France
11 Carnegie Institution of Washington, The Observatories, 813 Santa Barbara Street, Pasadena, CA 91101-1292,
USA
1
c ESO 2015
Astronomy & Astrophysics manuscript no. SUCCESS
July 1, 2015
New observations and models of circumstellar CO line emission of
AGB stars in the Herschel ? SUCCESS programme??
T. Danilovich1 , D. Teyssier2 , K. Justtanont1 , H. Olofsson1 , L. Cerrigone3 , V. Bujarrabal4 , J. Alcolea5 , J. Cernicharo6 ,
A. Castro-Carrizo7 , P. Garc´ıa-Lario2 , and A. Marston2
1
2
3
4
arXiv:1506.09065v1 [astro-ph.SR] 30 Jun 2015
5
6
7
Onsala Space Observatory, Department of Earth and Space Sciences, Chalmers University of Technology, 439 92 Onsala, Sweden
European Space Astronomy Centre, Urb. Villafranca del Castillo, PO Box 50727, 28080, Madrid, Spain
ASTRON, the Netherlands Institute for Radioastronomy, PO Box 2, 7990 AA, Dwingeloo, The Netherlands
Observatorio Astron´omico Nacional (IGN), PO Box 112, 28803 Alcal´a de Henares, Spain
Observatorio Astron´omico Nacional (IGN), Alfonso XII, 3 y 5, 28014 Madrid, Spain
Group of Molecular Astrophysics. ICMM. CSIC. C/ Sor Juana In´es de La Cruz N3. E-28049, Madrid. Spain
Institut de Radioastronomie Millim´etrique, 300 rue de la Piscine, F-38406, St-Martin d’H`eres, France
e-mail: [email protected]
Received 9 June 2015 / Accepted 28 June 2015
ABSTRACT
Context. Asymptotic giant branch (AGB) stars are in one of the latest evolutionary stages of low to intermediate-mass stars. Their
vigorous mass loss has a significant effect on the stellar evolution, and is a significant source of heavy elements and dust grains for
the interstellar medium. The mass-loss rate can be well traced by carbon monoxide (CO) line emission.
Aims. We present new Herschel HIFI and IRAM 30m telescope CO line data for a sample of 53 galactic AGB stars. The lines cover
a fairly large range of excitation energy from the J = 1 → 0 line to the J = 9 → 8 line, and even the J = 14 → 13 line in a few cases.
We perform radiative transfer modelling for 38 of these sources to estimate their mass-loss rates.
Methods. We used a radiative transfer code based on the Monte Carlo method to model the CO line emission. We assume spherically
symmetric circumstellar envelopes that are formed by a constant mass-loss rate through a smoothly accelerating wind.
Results. We find models that are consistent across a broad range of CO lines for most of the stars in our sample, i.e., a large number
of the circumstellar envelopes can be described with a constant mass-loss rate. We also find that an accelerating wind is required to
fit, in particular, the higher-J lines and that a velocity law will have a significant effect on the model line intensities. The results cover
a wide range of mass-loss rates (∼ 10−8 to 2 × 10−5 M yr−1 ) and gas expansion velocities (2 to 21.5 km s−1 ) , and include M-, S-, and
C-type AGB stars. Our results generally agree with those of earlier studies, although we tend to find slightly lower mass-loss rates by
about 40%, on average. We also present “bonus” lines detected during our CO observations.
Key words. Stars: AGB and post-AGB – circumstellar matter – stars: mass loss – stars: evolution
1. Introduction
Towards the end of their lives, low and intermediate mass stars
(with masses ∼ 0.8–8 M ) will exhaust their supply of He and
cease fusion reactions in their cores, leaving a quiescent C/O
core with H and He fusion reactions only taking place in thin
shells surrounding the core. This evolutionary phase is known as
the asymptotic giant branch (AGB) (Herwig 2005).
AGB stars are also a significant source of heavy elements in
the universe. It is thought that about half of all elements heavier than Fe originate in AGB stars through the s-process of slow
neutron capture (Herwig 2005). It is during the AGB phase that
this enriched material is brought to the surface. At the same time,
the star experiences vigorous mass loss, ejecting matter to form
a circumstellar envelope (CSE) around the star. Molecules and
dust grains form in the CSE, and will eventually chemically enrich the interstellar medium (ISM).
?
Herschel is an ESA space observatory with science instruments
provided by European-led Principal Investigator consortia and with important participation from NASA.
??
Based on observations carried out with the IRAM 30m Telescope.
IRAM is supported by INSU/CNRS (France), MPG (Germany) and
IGN (Spain).
It is believed that AGB stars begin their lives on the AGB as
oxygen-rich M-type stars, and eventually some of these, those
with masses in the range ∼ 1.5–4 M (Herwig 2005), will transition into carbon-rich C stars. With a C/O ratio close to 1, S
stars are believed to occupy the evolutionary phase between M
and C stars. The lowest mass AGB stars (. 1 M ) do not transform into C stars because they do not undergo a third dredge-up
event. The highest mass AGB stars (& 4 M ) also do not end
their lives as C stars due to hot bottom burning (HBB), unless
the mass loss quenches the HBB process, leaving time for the
star to evolve into a C star before leaving the AGB.
Radiative transfer modelling of circumstellar CO radio
lines has long been used to derive the mass-loss rates of
AGB stars (Morris 1987; Kastner 1992; Justtanont et al. 1994;
Groenewegen 1998; Sch¨oier & Olofsson 2001; Olofsson et al.
2002; Decin et al. 2006; Ramstedt et al. 2009; De Beck
et al. 2010). These data were almost exclusively obtained with
ground-based telescopes. The Herschel Space Observatory allowed observations of higher energy lines than possible from
ground-based telescopes. This has led to studies that model
molecular emission (not only that of CO) in more detail and over
a wide range of energies as in Sch¨oier et al. (2011), Khouri et al.
(2014), and Danilovich et al. (2014). However, each of those pa1
DRAFT: July 1, 2015
arXiv:1506.09056v1 [astro-ph.SR] 30 Jun 2015
Carbon-rich presolar grains from massive stars: subsolar
ratios and the mystery of 15 N
12
C/13 C and
14
N/15 N
M. Pignatari1,2,13 , E. Zinner3 , P. Hoppe4 , C.J. Jordan5,14 , B.K. Gibson5,14 , R. Trappitsch6,13
F. Herwig7,8,13 , C. Fryer9,13 , R. Hirschi10,11,13,14 , F. X. Timmes12,8,13
ABSTRACT
Carbon-rich grains with isotopic anomalies compared to the Sun are found in primitive meteorites. They were made by stars, and carry the original stellar nucleosynthesis
signature. Silicon carbide grains of Type X and C, and low-density graphites condensed
in the ejecta of core-collapse supernovae. We present a new set of models for the explosive He shell and compare them with the grains showing 12 C/13 C and 14 N/15 N ratios
lower than solar. In the stellar progenitor H was ingested into the He shell and not
fully destroyed before the explosion. Different explosion energies and H concentrations
are considered. If the SN shock hits the He-shell region with some H still present, the
models can reproduce the C and N isotopic signatures in C-rich grains. Hot-CNO cycle
isotopic signatures are obtained, including a large production of 13 C and 15 N. The
1
Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences,
Konkoly Thege Miklos ut 15-17, H-1121 Budapest, Hungary
2
Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
3
Laboratory for Space Sciences and Physics Department, Washington University, St. Louis, Mo 63130, USA
4
Max Planck Institute for Chemistry, D-55128 Mainz, Germany
5
E.A. Milne Centre for Astrophysics, Dept of Physics & Mathematics, University of Hull, HU6 7RX, United
Kingdom
6
Department of the Geophysical Sciences and Chicago Center for Cosmochemistry, Chicago, IL 60637, USA.
7
Department of Physics & Astronomy, University of Victoria, Victoria, BC, V8P5C2 Canada.
8
The Joint Institute for Nuclear Astrophysics, Notre Dame, IN 46556, USA
9
Computational Physics and Methods (CCS-2), LANL, Los Alamos, NM, 87545, USA.
10
Keele University, Keele, Staffordshire ST5 5BG, United Kingdom.
11
Institute for the Physics and Mathematics of the Universe (WPI), University of Tokyo, 5-1-5 Kashiwanoha,
Kashiwa 277-8583, Japan
12
Arizona State University (ASU), PO Box 871404, Tempe, AZ, 85287-1404, USA.
13
NuGrid collaboration, http://www.nugridstars.org
14
BRIDGCE UK Network, http://www.astro.keele.ac.uk/bridgce
c ESO 2015
Astronomy & Astrophysics manuscript no. 25707˙am-printer
July 1, 2015
A low-luminosity type-1 QSO sample
arXiv:1506.09053v1 [astro-ph.GA] 30 Jun 2015
III. Optical spectroscopic properties and activity classification
E.Tremou1,3 , M. Garcia-Marin1 , J. Zuther1 , A. Eckart1,2 , M. Valencia-Schneider1 , M. Vitale1,2 , C. Shan1
1
2
3
I.Physikalisches Institute, University of Cologne, Z¨ulpicher Strasse 77, 50937 Cologne, Germany
e-mail: [email protected]
Max Planck Institute for Radioastronomy, Auf dem H¨ugel 69, 53121 Bonn, Germany
Yonsei University Observatory, Yonsei University, Seoul 120-749, Republic of Korea
Received Month xx, 201x; accepted xxx x, 201x
ABSTRACT
Context. We report on the optical spectroscopic analysis of a sample of 99 low-luminosity quasi-stellar objects (LLQSOs) at z ≤ 0.06
base the Hamburg/ESO QSO survey (HES). To better relate the low-redshift active galactic nucleus (AGN) to the QSO population it is
important to study samples of the latter type at a level of detail similar to that of the low-redshift AGN. Powerful QSOs, however, are
absent at low redshifts due to evolutionary effects and their small space density. Our understanding of the (distant) QSO population
is, therefore, significantly limited by angular resolution and sensitivity. The LLQSOs presented here offer the possibility of studying
the faint end of this population at smaller cosmological distances and, therefore, in greater detail.
Aims. In comparing two spectroscopic methods, we aim to establish a reliable activity classification scheme of the LLQSOs sample.
Our goal is to enrich our systematic multiwavelength analysis of the AGN/starburst relation in these systems and give a complementary
information on this particular sample of LLQSOs from the Hamburg ESO survey.
Methods. Here, we present results of the analysis of visible wavelength spectroscopy provided by the HES and the 6 Degree Field
Galaxy Survey (6dFGS). These surveys use different spectroscopic techniques, long-slit and circular fiber, respectively. These allow
us to assess the influence of different apertures on the activity of the LLQSOs using classical optical diagnostic diagrams. We perform
a Gaussian fitting of strong optical emission lines and decompose narrow and broad Balmer components.
Results. A small number of our LLQSO present no broad component, which is likely to be present but buried in the noise. Two sources
show double broad components, whereas six comply with the classic NLS1 requirements. As expected in NLR of broad line AGNs,
the [Sii]−based electron density values range between 100 and 1000 Ne /cm3 . Using the optical characteristics of Populations A and B,
we find that 50% of our sources with Hβ broad emission are consistent with the radio-quiet sources definition. The remaining sources
could be interpreted as low-luminosity radio-loud quasar. The BPT-based classification renders an AGN/Seyfert activity between 50
to 60%. For the remaining sources, the possible starburst contribution might control the LINER and Hii classification. Finally, we
discuss the aperture effect as responsible for the differences found between data sets, although variability in the BLR could play a
significant role as well.
Key words. galaxies: Seyfert – quasars – starburst – emission lines
1. Introduction
Accretion of matter onto a supermassive black hole (SMBH) at
the center of a galaxy is the main energy source of galaxies hosting an active galactic nucleus (AGN). In a similar vein, the centers of starburst galaxies are not considered to be very active
in terms of nonthermal emission arising from nuclear accretion
and star formation processes originate the energy output instead.
However, the association between the AGN activity and the star
formation mechanism is still undetermined in galaxy evolution
scenarios. Hence, reliable classification frames are vital to establish the activity of the galaxies.
Classification of AGN depends upon many parameters.
Various studies focusing on selection criteria, morphology, and
line widths, have produced a variety of classification schemes
(e.g., Cid Fernandes et al. 2011; Ho 2008; Urry & Padovani
1995, and references therein). The emission line spectra of extragalactic sources has proven to be a reliable approach to diagnose the origin of the ionizing emission in a galaxy. In particular, the information contained in the relative intensities of the
emission lines in the visible domain have been used by Baldwin
et al. (1981, BPT diagrams), Veilleux & Osterbrock (1987a), and
more recently by Kewley et al. (2006a). The main idea is to discriminate between the different excitation mechanisms operating on the line emitting gas. Depending on the contribution of
the AGN, the galaxies can be categorized as quasi-stellar objects
(QSOs), from the high-power tail of the distribution in BPT diagrams down to Seyferts and low-ionization nuclear wmission
line eegions (LINERs; Heckman et al. 1980).
The nature of LINERs has been a long debate, with several explanations being offered to account for it. Ionization
by shocks was one of the first, (Heckman 1980), with young
hot stars being responsible for it (Terlevich & Melnick 1985;
Dopita & Sutherland 1995a). Pre-main sequence stars ionization (Cid Fernandes et al. 2004) have also been proposed as
ionization sources. Ionization by low-luminosity AGNs is a favored explanation (Ferland & Netzer 1983; Halpern & Steiner
1983; Ho et al. 1997b), in which case they would constitute
the main fraction of the AGN population. More recently, using radial emission-line surface brightness profiles, Singh et al.
(2013) found that the class of LINER galaxies are not generally
uniquely powered by a central AGN. They postulate that the ex1
Mon. Not. R. Astron. Soc. 000, 1–?? (2015)
Printed 1 July 2015
(MN LATEX style file v2.2)
arXiv:1506.09043v1 [astro-ph.EP] 30 Jun 2015
On the probability of the collision of a Mars-sized planet with the
Earth to form the Moon
Rudolf Dvorak⋆, Birgit Loibnegger, and Thomas I. Maindl
Department of Astrophysics, University of Vienna, T¨urkenschanzstrasse 17, 1180 Vienna
ABSTRACT
The problem of the formation of the Moon is still not explained satisfactorily. While it is a
generally accepted scenario that the last giant impact on Earth between some 50 to 100 million
years after the starting of the formation of the terrestrial planets formed our natural satellite,
there are still many open questions like the isotopic composition which is identical for these
two bodies. In our investigation we will not deal with these problems of chemical composition
but rather undertake a purely dynamical study to find out the probability of a Mars-sized body
to collide with the Earth shortly after the formation of the Earth-like planets. For that we
assume an additional massive body between Venus and Earth, respectively Earth and Mars
which formed there at the same time as the other terrestrial planets. We have undertaken
massive n-body integrations of such a planetary system with 4 inner planets (we excluded
Mercury but assumed one additional body as mentioned before) for up to tens of millions
of years. Our results led to a statistical estimation of the collision velocities as well as the
collision angles which will then serve as the basis of further investigation with detailed SPH
computations. We find a most probable origin of the Earth impactor at a semi-major axis of
approx. 1.16 AU.
Key words: celestial mechanics – planets and satellites: general - Moon
1 INTRODUCTION
An assumed giant impact of an additional Mars-sized object
(Theia) onto the Earth could have led to the formation of the Moon
after the planets already had their actual mass and no more gas
was present in the Solar System. Many recent publications deal
with this topic, e.g., Asphaug (2014), Nakajima & Stevenson
(2015), Quarles & Lissauer (2015), Jacobson et al (2014),
Jacobson & Morbidelli (2014) [=JM], Izidoro et al (2014),
since the first ideas developed by Hartmann & Davis (1975),
Cameron & Ward (1976), and later Canup & Asphaug (2001).
Detailed collision scenaria were studied e.g., by Cameron
(1997), Canup (2004), Canup (2008), and Canup (2013) where
the collision was modelled with the aid of sophisticated SPH
codes. In a most recent article Kaib & Cowan (2015) [=KC]
the authors concentrate on the feeding zone of the planet to
form with respect to the planet’s volatile inventory and isotopic
composition. Because of the highly random outcome they ask
the question of how deterministic the outcome of the planetary
formation is. In fact the correspondence of the results of the
different model computations of n-body codes is very small. Most
of these modelisations have been undertaken to understand the
architecture of our Solar System, which results only from a subset
of the chosen initial conditions. In KC the authors estimated the
⋆
E-mail: [email protected]
c 2015 RAS
likelihood that the mass of Theia could be equal to the mass of
the Earth, but the probability is rather low. Their results coincide
well with JM who estimated the collision probability of bodies
with comparable masses as being low. According to these results
we have fixed the mass of the additional planet (the ‘projectile
planet’) to mMars for our computations. Other investigations aimed
for high velocity encounters e.g. the one by Cuk et al (2012)
who assumed high velocity collisions for smaller masses of Theia
(0.025 mEarth < mTheia < 0.05 mEarth ), but the results of KC show
that such an event may not be very probable because a spin rate
of the Earth of the order of 2 hours can only be achieved by big
impactors – and these events are rare. Because of the same reason
the scenario proposed by Reufer et al (2012) where they look for
a steeper collision angle is not very probable. KC undertake 150
different simulations with 3 different underlying models: a first
model with Jupiter and Saturn on circular orbits, a second one with
initially small eccentricities of Jupiter and Saturn, and a third one
according to the model of Hansen (2009). Whereas in the first two
models 100 self interacting bodies (distributed between 0.5 and 4
AU with small eccentricities) were integrated which then end up as
planets, the last one starts with 400 embryos in an annulus between
0.7 and 1 AU and – according to the authors – represent more or
less the outcome of the Grand Tack model (Walsh et al 2012). It is
therefore appropriate to make such a study – which is orientated
versus the collision of a Mars-sized object with the Earth – on the
basis of these results.
Nuclear Physics B
Proceedings
Supplement
Nuclear Physics B Proceedings Supplement 00 (2015) 1–4
Shadow dark matter, sterile neutrinos and neutrino events at IceCube
Zurab Berezhiani
arXiv:1506.09040v1 [astro-ph.HE] 30 Jun 2015
Dipartimento di Fisica, Universit´a di L’Aquila and INFN, Laboratori Nazionali del Gran Sasso, L’Aquila, Italy
Abstract
The excess of high energy neutrinos observed by the IceCube collaboration might originate from baryon number
violating decays of heavy shadow baryons from dark mirror sector which produce shadow neutrinos. These sterile
neutrino species then oscillate into ordinary neutrinos transferring to them specific features of their spectrum. In
particular, this scenario can explain the end of the spectrum above 2 PeV or so and the presence of the energy gap
between 400 TeV and 1 PeV.
Recently the IceCube Collaboration published the
data on high-energy neutrinos collected between 2010
and 2013, containing 35 candidate events in the energy
range from 30 TeV to 2 PeV, which show an evident
excess over the expected background of the events with
E > 60−100 TeV or so [1]. On the other hand, no events
were observed in the gap between 400 TeV and 1 PeV
while three most energetic shower events emerged at
the end of the spectrum with energies between 1-2 PeV
where the atmospheric background is practically vanishing. The spectrum is apparently cut off at energies
larger than about 2 PeV. The gap in the energy spectrum
is difficult to explain in known models of high-energy
neutrinos of astrophysical origin.
Here we present a model [2] that may explain such
a spectrum. It is based on the idea that dark matter
of the universe emerges from a parallel gauge sector,
with particles and interactions sharing many similarities with ordinary particle sector. Such a shadow sector
would contain particles like quarks which form composite baryons, as well as leptons and neutrinos which are
all sterile for ordinary gauge interactions. Particularly
interesting example is represented by so-called mirror
world [3], which has the particle and interaction content exactly identical to that of ordinary sector, with the
same gauge and Yukawa coupling constants.
Taking into consideration also attractive possibilities
for physics beyond the Standard Model related to super-
symmetric (SUSY) grand unified theory (GUT), one can
consider that at higher energies our physics is presented
by SUSY GUT, e.g. S U(5) or S U(6) which breaks
down to the Standard Model S U(3)×S U(2)×U(1) at the
scale MG ' 2 × 1016 GeV. Supersymmetry breaking at
MSB ∼ 1 TeV triggers the electroweak symmetry breaking and the Higgs field gets the vacuum expectation
value (VEV) v = 174 GeV. In this view, we assume that
at higher energies also mirror sectors is presented by the
identical SUSY GUTs, S U(5)0 or S U(6)0 , which breaks
down to its standard subgroup S U(3)0 × S U(2)0 × U(1)0
at the same scale MG ' 2 × 1016 GeV. However, following refs. [4, 5], we assume that the symmetry
between two sectors is broken later so that the electroweak symmetry breaking scale v0 in mirror sector is
much larger than ordinary electroweak scale. Namely,
if v0 ∼ 1011 GeV, the lightest shadow baryons have
masses order few PeV, and they decay due to baryon
violating GUT gauge bosons, with decay time comparable to the age of the Universe, producing energetic
shadow neutrinos which then oscillate into active neutrinos (with oscillation probablities ∼ 10−9 or so) transferring their spectrum to the latter.1 It is worth to note that
the decaying dark matter model, with a fraction of dark
matter of about 10 per cent decaying before of present
epoch could reconcile the Planck collaboration results
1 For
other type of decaying dark matter model see e.g. Ref. [6].
arXiv:1506.09038v1 [astro-ph.GA] 30 Jun 2015
Dynamics of a Supernova Envelope in a Cloudy
Interstellar Medium∗
V. V. Korolev1 , E. O. Vasiliev2†, I. G. Kovalenko1 , Yu. A. Shchekinov3
1
Volgograd State University, Volgograd, Russia
2
Institute of Physics, Southern Federal University, Rostov-on-Don, Russia
3
Physics Department, Southern Federal University, Rostov-on-Don, Russia
Abstract
The evolution of a supernova remnant in a cloudy medium as a function of the volume
filling factor of the clouds is studied in a three-dimensional axially symmetrical model. The
model includes the mixing of heavy elements (metals) ejected by the supernova and their
contribution to radiative losses. The interaction of the supernova envelope with the cloudy
phase of the interstellar medium leads to nonsimultaneous, and on average earlier, onsets of
the radiative phase in different parts of the supernova envelope. Growth in the volume filling
factor f leads to a decrease in the time for the transition of the envelope to the radiative
phase and a decrease in the envelopes mean radius, due to the increased energy losses by the
envelope in the cloudy medium. When the development of hydrodynamical instabilities in the
supernova envelope is efficient, the thermal energy falls as Et ∼ t−2.3 , for the propagation of
the supernova remnant through either a homogeneous or a cloudy medium. When the volume
> 0.1, a layer with excess kinetic energy andmomentumforms far behind the
filling factor is f ∼
global shock front from the supernova, which traps the hot gas of the cavity in the central part
of the supernova remnant. Metals ejected by the supernova are also enclosed in the central
region of the remnant, where the initial (high) metallicity is essentially preserved. Thus,
the interaction of the supernova envelope with the cloudy interstellar medium appreciably
changes the dynamics and structure of the distribution of the gas in the remnant. This
affects the observational characteristics of the remnant, in particularly, leading to substantial
fluctuations of the emission measure of the gas with T > 105 K and the velocity dispersion
of the ionized gas.
1
Introduction
It is well known that the interstellar medium in galaxies is inhomogeneous and turbulent.
An appreciable role in maintaining the turbulent flows is played by supernova explosions (see,
e.g., [Elmegreen & Scalo(2004)]). The density contrast in these inhomogeneous media relative
to the mean density ranges from ∼ 1 (in a diffuse medium) to 1000 or more (in molecular
clouds). The interaction of shocks from supernovae with density inhomogeneities – clouds
– can give rise to compression, rarefaction, vaporization, and acceleration of these inhomogeneities [McKee & Ostriker(1977)]. The effects of the reverse influence of the clouds on the
dynamics of the supernova shocks are also evident. In spite of numerous numerical investigations of the disruption of individual clouds [Klein et al. (1994)] and ensembles of clouds
[Poludnenko et al. (2002)], some questions and details of the interaction process have not been
fully studied; in particular, the dependence of the remnant dynamics on the number of clouds
in the interstellar medium – the filling factor – has remained unclear.
∗
†
This paper is published in Astronomy Reports, 2015, Vol. 59, No. 7, pp. 690.
[email protected]
1
Librational solution for dust particles in mean motion resonances under the
action of stellar radiation
Pavol P´astor
arXiv:1506.09033v1 [astro-ph.EP] 30 Jun 2015
Tekov Observatory, Sokolovsk´
a 21, 934 01 Levice, Slovak Republic
[email protected], [email protected]
ABSTRACT
This paper presents a librational solution for evolutions of parameters averaged over
a synodic period in mean motion resonances in planar circular restricted three-body
problem (PCR3BP) with non-gravitational effects taken into account. The librational
solution is derived from a linearization of modified Lagrange’s planetary equations.
The presented derivation respects properties of orbital evolutions in the mean motion
resonances within the framework of the PCR3BP. All orbital evolutions in the PCR3BP
with the non-gravitational effects can be described by four varying parameters. We
used the semimajor axis, eccentricity, longitude of pericenter and resonant angular
variable. The evolutions are found for all four parameters. The solution can be applied
also in the case without the non-gravitational effects. We compared numerically and
analytically obtained evolutions in the case when the non-gravitational effects are the
Poynting-Robertson effect and the radial stellar wind. The librational solution is good
approximation when the libration amplitude of the resonant angular variable is small.
Subject headings: Interplanetary dust – Mean motion resonances – Celestial mechanics
– Poynting–Robertson effect, Stellar wind
1.
Introduction
Oscillations are often present when a physical system is near a stable state. The gravity of a
star and a planet (or a planet and a satellite) that move according to a solution of the two body
problem can perturb the motion of a body with negligible mass (restricted three-body problem).
The dynamic of the body with negligible mass includes in this case also the so called mean motion
resonances. In a mean motion resonance a ratio of orbital periods of the two minor bodies oscillates
near a ratio of two natural numbers.
The perturbed motion of the body captured in the mean motion resonance can be studied
using a disturbing function. The disturbing function is often expanded using Fourier series of the
Laplacian type (e.g., Murray & Dermott 1999). Usability of this access is limited by two factors.
First, a finite order of the expansion makes it practically unusable for large eccentricities. The
c
ESO
2015
Astronomy & Astrophysics manuscript no. n4418_scan_v4
July 1, 2015
Exploring the molecular chemistry and excitation in obscured
luminous infrared galaxies
An ALMA mm-wave spectral scan of NGC 4418
arXiv:1506.09027v1 [astro-ph.GA] 30 Jun 2015
F. Costagliola1, 3 , K. Sakamoto2 , S. Muller3 , S. Martín4 , S. Aalto3 , N. Harada2 , P. van der Werf5 , S. Viti6 , S.
Garcia-Burillo7 , and M. Spaans8
1
2
3
4
5
6
7
8
Istituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía, s/n, E-18008, Granada, Spain, e-mail:
[email protected]
Academia Sinica, Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan
Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala, Sweden
Institut de RadioAstronomie Millimétrique, 300 rue de la Piscine, Domaine Universitaire, 38406 Saint Martin d’Hères, France
Leiden Observatory, Leiden University, 2300 RA Leiden, The Netherlands
Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
Observatorio Astronómico Nacional (OAN)–Observatorio de Madrid, Alfonso XII 3, 28014 Madrid, Spain
Kapteyn Astronomical Institute, University of Gröningen, PO Box 800, 9700 AV Gröningen, The Netherlands
July 1, 2015
ABSTRACT
Context. Extragalactic observations allow the study of molecular chemistry and excitation under physical conditions which may differ
greatly from what found in the Milky Way. The compact, obscured nuclei (CON) of luminous infrared galaxies (LIRG) combine large
molecular columns with intense infrared (IR), ultra-violet (UV) and X- radiation and represent ideal laboratories to study the chemistry
of the interstellar medium (ISM) under extreme conditions.
Aims. To obtain for the first time a multi-band spectral scan of a LIRG, in order to derive the molecular abundances and excitation, to
be compared to other Galactic and extragalactic environments.
Methods. We obtained an ALMA Cycle 0 spectral scan of the dusty LIRG NGC 4418, spanning a total of 70.7 GHz in bands 3, 6,
and 7. We use a combined local thermal equilibrium (LTE) and non-LTE (NLTE) fit of the spectrum in order to identify the molecular
species and derive column densities and excitation temperatures. We derive molecular abundances and compare them with other
Galactic and extragalactic sources by means of a principal component analysis.
Results. We detect 317 emission lines from a total of 45 molecular species, including 15 isotopic substitutions and six vibrationally
excited variants. Our LTE/NLTE fit find kinetic temperatures from 20 to 350 K, and densities between 105 and 107 cm−3 . The spectrum
is dominated by vibrationally excited HC3 N, HCN, and HNC, with vibrational temperatures from 300 to 450 K. We find that the
chemistry of NCG 4418 is characterized by high abundances of HC3 N, SiO, H2 S, and c-HCCCH and a low CH3 OH abundance. A
principal component analysis shows that NGC 4418 and Arp 220 share very similar molecular abundances and excitation, which
clearly set them apart from other Galactic and extragalactic environments.
Conclusions. Our spectral scan confirms that the chemical complexity in the nucleus of NGC 4418 is one of the highest ever observed
outside our Galaxy. The similar molecular abundances observed towards NCG 4418 and Arp 220 are consistent with a hot gas-phase
chemistry, with the relative abundances of SiO and CH3 OH being regulated by shocks and X-ray driven dissociation. The bright
emission from vibrationally excited species confirms the presence of a compact IR source, with an effective diameter <5 pc and
brightness temperatures >350 K. The molecular abundances and the vibrationally excited spectrum are consistent with a young
AGN/starburst system. We suggest that NGC 4418 may be a template for a new kind of chemistry and excitation, typical of compact
obscured nuclei (CON). Because of the narrow line widths and bright molecular emission, NGC 4418 is the ideal target for further
studies of the chemistry in CONs.
Key words. galaxies: abundances – galaxies: ISM – galaxies: nuclei – galaxies: active – galaxies: individual: NGC 4418
1. Introduction
Extragalactic chemistry is a field that is quickly expanding leading to new, powerful diagnostic tools for the star-forming and active galactic nuclei (AGN) activity in galaxies (e.g., Meier et al.
2014; Viti et al. 2014; Martín et al. 2015). The extreme environments found in some extragalactic objects provide the opportunity of studying the properties of the interstellar medium
(ISM) beyond the typical conditions found in the Milky way.
Shocks, stellar- and AGN radiation, dust shielding, and cosmic
rays strongly impact the chemistry and excitation of the molecular ISM. Establishing the chemical and physical conditions of
the molecular gas becomes a particularly important identification tool when the activity itself is buried in dust.
A clear case is offered by the compact obscured nuclei
(CON) of IR-luminous (LIRGs) and ultraluminous galaxies
(ULIRGS, e.g., Sanders & Mirabel 1996). These galaxies radiate most of their energy as thermal dust emission in the infrared and constitute the dominant population among the most
luminous extragalactic objects. Observations at mid-IR and milArticle number, page 1 of 34
MNRAS 000, 1–12 (2015)
Preprint 1 July 2015
Compiled using MNRAS LATEX style file v3.0
Bayesian model selection without evidences: application to the dark
energy equation-of-state
Sonke
Hee,1,2? Will Handley,1,2 Mike P. Hobson1 , Anthony N. Lasenby1,2
1
arXiv:1506.09024v1 [astro-ph.CO] 30 Jun 2015
2
Astrophysics Group, Battcock Centre, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK
Kavli Institute for Cosmology Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
Last updated 2015 June 29; in original form 2015 June 29
ABSTRACT
A method is presented for Bayesian model selection without explicitly computing evidences,
by using a combined likelihood and introducing an integer model selection parameter n so
that Bayes factors, or more generally posterior odds ratios, may be read off directly from the
posterior of n. If the total number of models under consideration is specified a priori, the
full joint parameter space (θ, n) of the models is of fixed dimensionality and can be explored
using standard MCMC or nested sampling methods, without the need for reversible jump
MCMC techniques. The posterior on n is then obtained by straightforward marginalisation.
We demonstrate the efficacy of our approach by application to several toy models. We then
apply it to constraining the dark energy equation-of-state using a free-form reconstruction
technique. We show that ΛCDM is significantly favoured over all extensions, including the
simple w(z)=constant model.
Key words: methods: statistical – methods: data analysis – dark energy – equation of state –
cosmological parameters
1
INTRODUCTION
Comparing two or more models given some data is central to the
scientific method. The field of model selection within statistical inference attempts to address this problem, and numerous techniques
for choosing between models exist, including: Akaike’s Information Criterion (Akaike 1974), Schwarz’s Bayesian Information Criterion (Schwarz 1978) and the Bayesian evidence (Jeffreys 1961;
MacKay 2003). Here we focus on Bayesian model selection using
the evidence Z (also known as the prior predictive or marginal likelihood) and posterior odds ratios Pi j (a generalisation of the more
commonly used Bayes Factors Bi j ), as this technique is inherent
to Bayes theorem and both are widely used throughout cosmology
and astrophysics (Liddle et al. 2006).
Posterior odds ratios provide a quantitative means for selecting between models and are usually calculated directly from the
evidence of each model. In higher dimensions, techniques to calculate evidences include thermodynamic integration (also known
as simulated annealing) (Gelman & Meng 1998), approximations
to the evidence when certain favourable conditions are met (such
as unimodality and Gaussianity) (Gelman & Meng 1998; Liddle
et al. 2006) and nested sampling (Sivia & Skilling 2006; Skilling
2004, 2006). Calculating Bayes factors directly, without calculating Z for each model, is also possible using the Savage-Dickey
density ratio for nested models (where a more complex model reduces to the simpler by setting its additional parameters appropri?
Contact e-mail: [email protected]
c 2015 The Authors
ately) (Verdinelli & Wasserman 1995). A good review from before
nested sampling’s rise in popularity can be found in Clyde et al.
(2007); for a thorough review of these methods in cosmology see
Trotta (2008).
In this paper we propose a method to calculate posterior odds
ratios without the problems associated with evidence calculations
or simplifying assumptions. Posterior odds ratios are calculated directly from a set of models explored simultaneously without constraints on the forms these models might take. The new method circumvents the challenges associated with accurate evidence calculations by computing posterior odds ratios using Bayesian parameter
estimation, which is typically a more reliable and computationally
less expensive task. Additionally, parameter estimation algorithms
are more commonly used and therefore the method provides an
easy means for extending existing codes to the domain of model
selection. This is achieved by introducing a parameter that selects
between models, and allows the calculation of posterior odds ratios
from the posterior probability of this parameter. We note that similar approaches have been proposed previously (Hobson & McLachlan 2003; Goyder & Lasenby 2004; Brewer & Donovan 2015), but
these typically rely on the use of sampling techniques capable of
jumping between parameter spaces of different sizes, such as reversible jump MCMC (Green 1995), which requires special sampling methods that are often very computationally demanding. Our
approach is much simpler, requiring no special sampling methods,
provided the number of models under consideration is specified a
priori.
We apply our method to toy models and the cosmological
Astronomy & Astrophysics manuscript no. h_flux_comparison_2Col
July 1, 2015
c
ESO
2015
Testing magnetic helicity conservation in a solar-like active event
arXiv:1506.09013v1 [astro-ph.SR] 30 Jun 2015
E. Pariat1 , G. Valori2 , P. Démoulin1 , and K. Dalmasse3,1
1
LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot,
Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France e-mail: [email protected]
2
UCL-Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
3
CISL/HAO, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000, USA
Received ***; accepted ***
ABSTRACT
Context. Magnetic helicity has the remarkable property of being a conserved quantity of ideal magnetohydrodynamics (MHD).
Therefore, it could be used as an effective tracer of the magnetic field evolution of magnetised plasmas.
Aims. Theoretical estimations indicate that magnetic helicity is also essentially conserved with non-ideal MHD processes, e.g. magnetic reconnection. This conjecture has however been barely tested, either experimentally or numerically. Thanks to recent advances
in magnetic helicity estimation methods, it is now possible to test numerically its dissipation level in general three-dimensional
datasets.
Methods. We first revisit the general formulation of the temporal variation of relative magnetic helicity on a fully bounded volume
when no hypothesis on the gauge is made. We introduce a method to precisely estimate its dissipation independently of the type of
non-ideal MHD processes occurring. In a solar-like eruptive event simulation, using different gauges, we compare its estimation in a
finite volume with its time-integrated flux through the boundaries, hence testing the conservation and dissipation of helicity.
Results. We provide an upper bound of the real dissipation of magnetic helicity: It is quasi-null during the quasi-ideal MHD phase.
Even when magnetic reconnection is acting the relative dissipation of magnetic helicity is also very small (< 2.2%), in particular
compared to the relative dissipation of magnetic energy (> 30 times larger). We finally illustrate how the helicity-flux terms involving
velocity components are gauge dependent, hence limiting their physical meaning.
Conclusions. Our study paves the way for more extended and diverse tests of the magnetic helicity conservation properties. Our
study confirms the central role that helicity can play in the study of MHD plasmas. For instance, the conservation of helicity can be
used to track the evolution of solar magnetic fields, from its formation in the solar interior until their detection as magnetic cloud in
the interplanetary space.
Key words. Magnetic fields, Methods: numerical, Sun: surface magnetism, Sun: corona
1. Introduction
In physics, conservation principle have driven the understanding of observed phenomena. Exact and even approximately conserved quantities have allowed to better describe and predict the
behaviour of physical systems. Conservation laws state that, for
an isolated system, a particular measurable scalar quantity does
not change as the system evolves. A corollary is that for a non
isolated system, a conserved scalar quantity only evolves thanks
to the flux of that quantity through the studied system boundaries. Given a physical paradigm, a physical quantity may not
be conserved if source or dissipation terms exist.
In the magnetohydrodynamics (MHD) framework, a quantity has received increasing attention for its conservation property: magnetic helicity (Elsasser 1956). Magnetic helicity quantitatively describes the geometrical degree of twist, shear, or
more generally, knottedness of magnetic field lines (Moffatt
1969). In ideal MHD, where magnetic field can be described
as the collection of individual magnetic field lines, magnetic helicity is a strictly conserved quantity (Woltjer 1958) as no dissipation, nor creation, of helicity is permitted since magnetic field
line cannot reconnect.
In his seminal work, Taylor (1974) conjectured that even in
non-ideal MHD, the dissipation of magnetic helicity should be
relatively weak, and hence, that magnetic helicity should be conserved. This could be theoretically explained by the inversecascade property of magnetic helicity: in turbulent medium,
helicity unlike magnetic energy, tends to cascade towards the
larger spatial scales, thus avoiding dissipation at smaller scales
(Frisch et al. 1975; Pouquet et al. 1976). This cascade has
been observed in numerical simulations (Alexakis et al. 2006;
Mininni 2007) as well as in laboratory experiments (Ji et al.
1995). In the case of resistive MHD, Berger (1984) derived an
upper limit on the amount of magnetic helicity that could be dissipated through constant resistivity. He showed that the typical
helicity dissipation time in the solar corona was far exceeding
the one for magnetic energy dissipation.
From the Taylor’s conjecture on helicity conservation have
been derived multiple important consequences for the dynamics of plasma systems. Based on helicity conservation, Taylor
(1974) predicted that relaxing MHD systems should reach
a linear force free state. This prediction, which was verified to different degrees, has allowed to understand the dynamics of plasma in several laboratory experiments (Taylor
Article number, page 1 of 16
Astronomy & Astrophysics manuscript no. giano˙sky˙continuum˙v08
July 1, 2015
c ESO 2015
Lines and continuum sky emission in the near infrared:
observational constraints from deep high spectral resolution
spectra with GIANO-TNG⋆
arXiv:1506.09004v1 [astro-ph.IM] 30 Jun 2015
E. Oliva1 , L. Origlia2 , S. Scuderi3 , S. Benatti4 , I. Carleo4 , E. Lapenna5 , A. Mucciarelli5 , C. Baffa1 , V. Biliotti1 , L.
Carbonaro1 , G. Falcini1 , E. Giani1 , M. Iuzzolino1 , F. Massi1 , N. Sanna1 , M. Sozzi1 , A. Tozzi1 , A. Ghedina6 , F.
Ghinassi6 , M. Lodi6 , A. Harutyunyan6 , and M. Pedani6
1
2
3
4
5
6
INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy
e-mail: [email protected]
INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna, Italy
INAF - Osservatorio Astrofisico di Catania, via S. Sofia 78, I-95123 Catania, Italy
INAF - Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, I-35122 Padova, Italy
Universit`a di Bologna, Dipartimento di Fisica e Astronomia, Viale Berti Pichat 6/2, I-40127 Bologna, Italy
INAF - Fundaci´on Galileo Galilei, Rambla Jos´e Ana Fern´andez P´erez 7, E-38712 Bre˜na Baja, TF, Spain
Received .... ; accepted ...
ABSTRACT
Aims. Determining the intensity of lines and continuum airglow emission in the H-band is important for the design of faint-object
infrared spectrographs. Existing spectra at low/medium resolution cannot disentangle the true sky-continuum from instrumental
effects (e.g. diffuse light in the wings of strong lines). We aim to obtain, for the first time, a high resolution infrared spectrum deep
enough to set significant constraints on the continuum emission between the lines in the H-band.
Methods. During the second commissioning run of the GIANO high-resolution infrared spectrograph at the La Palma Observatory,
we pointed the instrument directly to the sky and obtained a deep spectrum that extends from 0.97 to 2.4 µm.
Results. The spectrum shows about 1500 emission lines, a factor of two more than in previous works. Of these, 80% are identified
as OH transitions; half of these are from highly excited molecules (hot-OH component) that are not included in the OH airglow
emission models normally used for astronomical applications. The other lines are attributable to O2 or unidentified. Several of the
faint lines are in spectral regions that were previously believed to be free of line emission. The continuum in the H-band is marginally
detected at a level of about 300 photons/m2 /s/arcsec2 /µm, equivalent to 20.1 AB-mag/arcsec2 . The observed spectrum and the list of
observed sky-lines are published in electronic format.
Conclusions. Our measurements indicate that the sky continuum in the H-band could be even darker than previously believed.
However, the myriad of airglow emission lines severely limits the spectral ranges where very low background can be effectively
achieved with low/medium resolution spectrographs. We identify a few spectral bands that could still remain quite dark at the
resolving power foreseen for VLT-MOONS (R≃6,600).
Key words. Line: identification – Instrumentation: spectrograph – Infrared: general – Techniques: spectroscopic
1. Introduction
The sky emission spectrum at infrared wavelengths and up to
1.8 µm (Y, J, H bands) is dominated by lines (airglow) emitted
by OH and O2 molecules; see e.g. Sharma 1985. These lines are
intrinsically very narrow and, when observed at a high enough
spectral resolution, they occupy only a small fraction of the spectrum. Therefore, by filtering the lines out, one could in principle decrease the sky background by orders of magnitudes, down
to the level set by the sky continuum emission in between the
lines. This apparently simple idea, often reported as ”OH skysuppression”, has fostered a long and active field of research;
see e.g. Oliva & Origlia 1992, Maihara et al. 1993, Herbst 1994,
Content 1996, Ennico et al. 1998, Cuby et al. 2000, Rousselot
et al. 2000, Iwamuro et al. 2001, Bland-Hawthorn et al. 2004,
⋆
Tables 1, 2, and 4 are only available at the CDS via
anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/vol/page
Iwamuro et al. 2006, Ellis et al. 2012, Trinh et al. 2013. However,
in spite of the intense work devoted to measuring and modelling
the properties of the sky spectrum, it is still not clear what is the
real level of the sky continuum in between the airglow lines in
the H-band (1.5-1.8 µm).
A detailed study of the infrared sky continuum emission was
recently reported by Sullivan & Simcoe 2012. Using spectra at
a resolving power R=6,000 they were able to correct the spectra for all instrumental effects and derive accurate measurements
of the sky continuum at wavelengths shorter than 1.3 µm (Y,
J bands). However, they could not obtain precise results in the
H-band (1.5-1.8 µm) because the sky continuum is well below
the light diffused in the instrumental wings of the airglow lines.
This problem was already noted in earlier works. In particular,
Bland-Hawthorn et al. 2004 claimed that the continuum level between the OH lines could be as low as the zodiacal light level and
much lower than that measurable with classical (i.e. not properly
OH suppressed) spectrographs. This claim was later retracted by
1
c
ESO
2015
Astronomy & Astrophysics manuscript no. ms_swj050819
July 1, 2015
AGN feedback in action: a new powerful wind in
1SXPS J050819.8+172149? ⋆
L. Ballo1⋆⋆ , P. Severgnini1 , V. Braito2, 3 , S. Campana2 , R. Della Ceca1 , A. Moretti1 , and C. Vignali4, 5
1
2
3
arXiv:1506.09002v1 [astro-ph.HE] 30 Jun 2015
4
5
Osservatorio Astronomico di Brera (INAF), via Brera 28, I-20121, Milano (Italy)
Osservatorio Astronomico di Brera (INAF), via E. Bianchi 46, I-23807 Merate, LC (Italy)
Department of Physics, University of Maryland, Baltimore County, Baltimore, MD 21250 (USA)
Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, viale Berti Pichat 6/2, I-40127, Bologna (Italy)
Osservatorio Astronomico di Bologna (INAF), Via Ranzani 1, I-40127, Bologna (Italy)
Received 21 May 2015 / Accepted 29 June 2015
ABSTRACT
Context. Galaxy merging is widely accepted to be a key driving factor in galaxy formation and evolution, while the feedback from
actively accreting nuclei is thought to regulate the black hole-bulge coevolution and the star formation process.
Aims. In this context, we focused on 1SXPS J050819.8+172149, a local (z = 0.0175) Seyfert 1.9 galaxy (L bol ∼ 4 × 1043 ergs s−1 ).
The source belongs to an infrared-luminous interacting pair of galaxies, characterized by a luminosity for the whole system (due to the
combination of star formation and accretion) of log(L IR /L ⊙ ) = 11.2. We present here the first detailed description of the 0.3 − 10 keV
spectrum of 1SXPS J050819.8+172149, monitored by Swift with 9 pointings performed in less than 1 month.
Methods. The X-ray emission of 1SXPS J050819.8+172149 is analysed by combining all the Swift pointings, for a total of ∼ 72 ks
XRT net exposure. The averaged Swift-BAT spectrum from the 70-month survey is also analysed.
Results. The slope of the continuum is Γ ∼ 1.8, with an intrinsic column density of ∼ 2.4 × 1022 cm−2 , and a de-absorbed luminosity
of ∼ 4 × 1042 ergs s−1 in the 2 − 10 keV band. Our observations provide a tentative (2.1σ) detection of a blue-shifted Fe xxvi absorption
line (rest-frame E ∼ 7.8 keV), thus suggesting the discovery for a new candidate powerful wind in 1SXPS J050819.8+172149. The
physical properties of the outflow cannot be firmly assessed, due to the low statistics of the spectrum and to the observed energy of the
line, too close to the higher boundary of the Swift-XRT bandpass. However, our analysis suggests that, if the detection is confirmed,
the line could be associated with a high-velocity (v out ∼ 0.1c) outflow most likely launched within 80 r S . To our knowledge this is
the first detection of a previously unknown ultrafast wind with Swift. The high column density suggested by the observed equivalent
width of the line (EW∼ −230 eV, although with large uncertainties), would imply a kinetic output strong enough to be comparable to
the AGN bolometric luminosity.
Key words. galaxies: active - X-rays: individuals: 1SXPS J050819.8+172149 - quasars: absorption lines - galaxies: star formation
1. Introduction
The observational evidence for the presence of inactive Super
Massive Black Holes (SMBHs; M BH ∼ 106 − 1010 M ⊙ ) at the
centre of most, if not all, the local galaxies, and the observed
correlation between several properties of the galaxy’s bulge and
the central SMBH mass (Ferrarese & Merritt 2000; Gebhardt
et al. 2000), suggest that the SMBH accretion and the assembly
of the galaxies bulges are intimately related (see Kormendy &
Ho 2013, for a recent review). Funnelling of gas in the nuclear
regions, as triggered by galaxy interactions, can activate both
efficient accretion onto the SMBH, and a burst of star formation. A key ingredient in regulating their evolution should be the
feedback from the Active Galactic Nuclei (AGN); being conservative, while building its mass the SMBH can release an amount
of energy larger than ∼ 30 times the binding energy of the host
bulge (see a review in Fabian 2012). Even if only a small fraction of this energy is transferred to the gas in the galaxy, then
an active nucleus can have a profound effect on the evolution
of its host (Di Matteo et al. 2005). Powerful (kinetical or radiative) outflows of gas driven by luminous quasars are invoked as
⋆
⋆⋆
Based on observations obtained with the Swift satellite.
E-mail: [email protected] (LB)
a key mechanism to blow away the gas in the galaxy and thereby
quench star formation, coincidentally starving the SMBH of fuel
(King & Pounds 2015).
AGN winds with a range of physical properties have been
revealed by observations at various energies, from radio up to
X-rays. Outflows of molecular or neutral atomic gas, with velocities up to ∼ 1000 − 2000 km s−1 and extending on kpc scales,
have been observed at mm (e.g., Feruglio et al. 2010; Cicone
et al. 2014) and radio frequencies (e.g., Morganti et al. 2005;
Teng et al. 2013) in a few dozen AGN in dusty star forming sources and/or radio galaxies. Mass outflows of ionized gas
with similar velocities at distances consistent with the narrow
line region zone have been detected in the optical/ultraviolet
(UV), both in the [O iii] emission line profiles (e.g., Crenshaw
& Kraemer 2005; Cano-Díaz et al. 2012; Cresci et al. 2015),
and through the observation of broad absorption line systems
(e.g., Dai et al. 2008; Borguet et al. 2013). In X-rays, mildly
ionized warm absorbers are observed in more than half of unobscured AGN (Crenshaw et al. 2003; Blustin et al. 2005). The observed velocities of ∼ 500 − 1000 km s−1 imply a kinetic power
rather low when compared to the bolometric luminosity. However, Crenshaw & Kraemer (2012) found that, when summed
over all the absorbers, the total power carried by these structures
Article number, page 1 of 6
Mon. Not. R. Astron. Soc. 000, 1–14 (2013)
Printed 1 July 2015
(MN LATEX style file v2.2)
He-Accreting WDs: AM CVn stars with WD Donors
arXiv:1506.08976v1 [astro-ph.SR] 30 Jun 2015
L.
Piersanti1,4⋆ and L.R. Yungelson2 and A. Tornamb´e3
1
INAF-Osservatorio Astronomico di Collurania Teramo via Mentore Maggini, snc, 64100, Teramo, IT
of Astronomy, Pyatnitskaya 48, 119017 Moscow, Russia
3 INAF-Osservatorio Astronomico di Roma via di Frascati, 33, 00040, Monte Porzio Catone, IT
4 INFN-Sezione di Napoli, 80126 Napoli, Italy
2 Institute
1 July 2015
ABSTRACT
We study the physical and evolutionary properties of the “WD family” of AM CVn stars
by computing realistic models of Interacting Double-Degenerate systems. We evaluate selfconsistently both the mass transfer rate from the donor, as determined by gravitational wave
emission and interaction with the binary companion, and the thermal response of the accretor
to mass deposition. We find that, after the onset of mass transfer, all the considered systems
undergo a strong non-dynamical He-flash. However, due to the compactness of these systems,
the expanding accretors fill their Roche lobe very soon, thus preventing the efficient heating
of the external layers of the accreted CO WDs. Moreover, due to the loss of matter from
the systems, the orbital separations enlarge and mass transfer comes to a halt. The further
˙ after the donors fill again their lobe. On one hand,
evolution depends on the value of M
if the accretion rate, as determined by the actual value of (Mdon , Macc ), is high enough,
the accretors experience several He-flashes of decreasing strength and then quiescent Heburning sets in. Later on, since the mass transfer rate in IDD is a permanently decreasing
function of time, accretors experience several recurrent strong flashes. On the other hand, for
˙ the accretors enter directly the strong flashes accretion
intermediate and low values of M
regime. As expected, in all the considered systems the last He-flash is the strongest one,
even if the physical conditions suitable for a dynamical event are never attained. When the
mass accretion rate decreases below (2 − 3) × 10−8 M⊙ yr−1 , the compressional heating of
the He-shell becomes less efficient than the neutrino cooling, so that all the accretors in the
considered systems evolve into massive degenerate objects. Our results suggest that SN .Ia or
type Ia Supernovae due to Edge-Lit Detonation in the WD family of AM CVn stars should
be much more rare than previously expected.
Key words: Binaries: general, Supernovae:general, White Dwarfs, Accretion
1 INTRODUCTION
AM CVn stars are ultracompact cataclysmic binaries with spectra dominated by helium. At the time of writing 43 confirmed and
candidate objects were known, see Table 1 in Levitan et al. (2015),
and Wagner et al. (2014); Kato, Hambsch & Monard (2015). Measured orbital periods range from 5.5 to 65 min. There exist also
several cataclysmic variables (some with hydrogen-deficient spectra) below the conventional minimum Porb of CV (70-80) min.,
which may be AM CVn stars in making (Breedt et al. 2012;
Carter et al. 2013b; Littlefield et al. 2013; Ramsay et al. 2014;
Garnavich et al. 2014). The significance of AM CVn stars stems
from their importance for the studies of very late stages of evolution of binary stars and of accretion disks physics; as well
they are considered primary targets and verification sources for
⋆
E-mail: [email protected] (LP); [email protected]
(AT); [email protected] (LY)
© 2013 RAS
high-frequency gravitational waves detectors. The current models of AM CVn stars envision a semidetached binary harbouring
a carbon-oxygen white dwarf (CO WD) accreting He-rich matter. The donor may be either a helium WD or a low-mass helium
star or a core of a main-sequence star strongly evolved prior to
Roche-lobe overflow (RLOF). The evolution of AM CVn binaries
is driven by angular momentum loss via gravitational waves radiation (GWR). An overview and a discussion of observational features, formation and evolution of these stars, as well as models
for their disks may be found, e. g., in Warner (2003); Nelemans
(2005, 2009); Solheim (2010); Ruiter et al. (2010); Kotko et al.
(2012); Amaro-Seoane et al. (2013); Postnov & Yungelson (2014);
Cannizzo & Nelemans (2015). The topic of the present study are
AM CVn systems with WD donors, sometimes also called “interacting double-degenerates” (IDD) or “white-dwarf family of
AM CVn stars”.
An essential issue defining the formation of AM CVn
stars is stability of mass-transfer by degenerate donors
arXiv:1506.08965v1 [astro-ph.SR] 30 Jun 2015
Resonant Absorption of Transverse Oscillations and Associated
Heating in a Solar Prominence. I- Observational aspects
Takenori J. Okamoto,1,8 Patrick Antolin,2 Bart De Pontieu,3,4 Han
Uitenbroek,5 Tom Van Doorsselaere,6 Takaaki Yokoyama7
1
ISAS/JAXA, Sagamihara, Kanagawa 252-5210, Japan
National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan
3
Lockheed Martin Solar and Astrophysics Laboratory, B/252, 3251 Hanover St., Palo Alto,
CA 94304, USA
4
Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315
Oslo, Norway
5
National Solar Observatory, PO Box 62, Sunspot, NM 88349, USA
6
Centre for Mathematical Plasma Astrophysics, Mathematics Department, KU Leuven,
Celestijnenlaan 200B bus 2400, B-3001 Leuven, Belgium
7
The University of Tokyo, Hongo, Bunkyo, Tokyo 113-0033, Japan
2
[email protected]
ABSTRACT
Transverse magnetohydrodynamic (MHD) waves have been shown to be ubiquitous in the solar atmosphere and can in principle carry sufficient energy to generate and maintain the Sun’s million-degree outer atmosphere or corona. However, direct evidence of the dissipation process of these waves and subsequent
heating has not yet been directly observed. Here we report on high spatial, temporal, and spectral resolution observations of a solar prominence that show a
compelling signature of so-called resonant absorption, a long hypothesized mechanism to efficiently convert and dissipate transverse wave energy into heat. Aside
from coherence in the transverse direction, our observations show telltale phase
differences around 180◦ between transverse motions in the plane-of-sky and lineof-sight velocities of the oscillating fine structures or threads, and also suggest
significant heating from chromospheric to higher temperatures. Comparison with
advanced numerical simulations support a scenario in which transverse oscillations trigger a Kelvin-Helmholtz instability (KHI) at the boundaries of oscillating
threads via resonant absorption. This instability leads to numerous thin current
8
Current address: STEL, Nagoya University, Aichi 464-8601, Japan
Mon. Not. R. Astron. Soc. 000, 1–5 ()
Printed 1 July 2015
(MN LATEX style file v2.2)
arXiv:1506.08957v1 [astro-ph.GA] 30 Jun 2015
Quantifying AGN-Driven Metal-Enhanced Outflows in
Chemodynamical Simulations
Philip Taylor1⋆ and Chiaki Kobayashi1,2
1 Centre
for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, AL10 9AB, UK
Visitor at Research School of Astronomy and Astrophysics, The Australian National University, Australia
2 Distinguished
Accepted Received ; in original form
ABSTRACT
We show the effects of AGN-driven outflows on the ejection of heavy elements using our cosmological simulations, where super-massive black holes originate from the first stars. In the
most massive galaxy, we have identified two strong outflows unambiguously driven by AGN
feedback. These outflows have a speed greater than ∼ 8000 km s−1 near the AGN, and travel
out to a half Mpc with ∼ 3000 km s−1 . These outflows remove the remaining gas (∼ 3 per
cent of baryons) and significant amounts of metals (∼ 2 per cent of total produced metals)
from the host galaxy, chemically enriching the circumgalactic medium (CGM) and the intergalactic medium (IGM). 17.6 per cent of metals from this galaxy, and 18.4 per cent of total
produced metals in the simulation, end up in the CGM and IGM, respectively. The metallicities of the CGM and IGM are higher with AGN feedback, while the mass–metallicity relation
of galaxies is not affected very much. We also find ‘selective’ mass-loss where iron is more
effectively ejected than oxygen because of the time-delay of Type Ia Supernovae. AGN-driven
outflows play an essential role not only in quenching of star formation in massive galaxies to
match with observed down-sizing phenomena, but also in a large-scale chemical enrichment
in the Universe. Observational constraints of metallicities and elemental abundance ratios in
outflows are important to test the modelling of AGN feedback in galaxy formation.
Key words: black hole physics – galaxies: evolution – galaxies: formation – methods: numerical – galaxies: abundances
1 INTRODUCTION
The importance of feedback from active galactic nuclei (AGN) has
been underscored by the discovery of the relationship between the
mass of the central black hole (BH) and the mass of the host galaxy
bulge (Magorrian et al. 1998; Kormendy & Ho 2013), suggesting
co-evolution of BHs and their host galaxies. This has already been
indicated from the similar shapes between the observed cosmic star
formation history (e.g., Madau et al. 1996) and the quasar space
density (e.g., Schmidt et al. 1995). AGN feedback has been implemented in cosmological simulations, which provided an excellent agreement with the Magorrian relation (e.g., Di Matteo et al.
2008; Sijacki et al. 2014) and a better reproduction of the cosmic
star formation rates (e.g., Taylor & Kobayashi (2014, hereafter
TK14), Vogelsberger et al. 2014). The [α/Fe] problem in early-type
galaxies also requires AGN feedback, which plays an essential role
in quenching star formation in massive galaxies where supernova
(SN) feedback is inefficient (Taylor & Kobayashi 2015, hereafter
TK15).
For the quenching mechanism, SN-driven galactic winds have
⋆
E-mail:[email protected]
c RAS
been proposed (Larson 1974; Arimoto & Yoshii 1987), but are not
efficient enough for massive galaxies in hydrodynamical simulations with dark matter (e.g., Kobayashi 2005; Kobayashi et al.
2007). There is observational evidence for galactic winds both locally and at high redshifts, from low-mass star-forming galaxies
(e.g., M82, Ohyama et al. 2002) to AGN-hosting massive galaxies (e.g., Centaurus A, Kraft et al. 2009). Supernova-driven winds
typically have velocities of a few 102 − 103 km s−1 and an outflow rate comparable to the star formation rate (e.g., Heckman et al.
2000; Pettini et al. 2000), while AGN-driven winds show much
higher velocities and outflow rates. The presence of outflows in
luminous quasars and AGN has been evidenced in broad absorption lines (Lynds 1967). The nearest quasar Mrk 231 shows a
multi-phase outflow containing ionized, neutral (Rupke & Veilleux
2013; Teng et al. 2014), and molecular gas (Feruglio et al. 2010;
Cicone et al. 2012), which may be explained by a bipolar outflow
and an accretion disk. Winds are also seen in Seyfert galaxies (e.g.,
Tombesi et al. 2011, 2013; Pounds & King 2013; Pounds 2014), in
which velocity probably depends on the distance from the central
BHs on ∼pc to ∼kpc scales (Tombesi et al. 2013), and in other ultraluminous infrared galaxies with velocities depending not on star
formation rate but on AGN luminosity (Sturm et al. 2011). At high
D RAFT VERSION J ULY 1, 2015
Preprint typeset using LATEX style emulateapj v. 2/19/04
arXiv:1506.08931v1 [astro-ph.GA] 30 Jun 2015
OSCILLATING RED GIANTS OBSERVED DURING CAMPAIGN 1 OF THE KEPLER K2 MISSION: NEW PROSPECTS
FOR GALACTIC ARCHAEOLOGY
D ENNIS S TELLO 1,2 , DANIEL H UBER 1,3,2 , S ANJIB S HARMA 1 , J ENNIFER J OHNSON 4 , M IKKEL N. L UND 2 , R ASMUS H ANDBERG 2 ,
D EREK L. B UZASI 5 , V ICTOR S ILVA AGUIRRE 2 , W ILLIAM J. C HAPLIN 6,2 , A NDREA M IGLIO 6,2 , M ARC P INSONNEAULT 4,
S ARBANI BASU 7 , T IM R. B EDDING 1,2 , J OSS B LAND -H AWTHORN 1 , L UCA C ASAGRANDE 8 , G UY DAVIES 6,2 , Y VONNE E LSWORTH 6,2 ,
R AFAEL A. G ARCIA 9 , S AVITA M ATHUR 10 , M ARIA P IA D I M AURO 11 , B ENOIT M OSSER 12 , D ONALD P. S CHNEIDER 13,14 ,
A LDO S ERENELLI 15, AND M ARICA VALENTINI 16
Draft version July 1, 2015
ABSTRACT
NASA’s re-purposed Kepler mission – dubbed K2 – has brought new scientific opportunities that were not
anticipated for the original Kepler mission. One science goal that makes optimal use of K2’s capabilities, in
particular its 360-degree ecliptic field of view, is galactic archaeology – the study of the evolution of the Galaxy
from the fossil stellar record. The thrust of this research is to exploit high-precision, time-resolved photometry
from K2 in order to detect oscillations in red giant stars. This asteroseismic information can provide estimates
of stellar radius (hence distance), mass and age of vast numbers of stars across the Galaxy. Here we present the
initial analysis of a subset of red giants, observed towards the North Galactic Gap, during the mission’s first
full science campaign. We investigate the feasibility of using K2 data for detecting oscillations in red giants
that span a range in apparent magnitude and evolutionary state (hence intrinsic luminosity). We demonstrate
that oscillations are detectable for essentially all cool giants within the log g range ∼ 1.9–3.2. Our detection is
complete down to Kp ∼ 14.5, which results in a seismic sample with little or no detection bias. This sample
is ideally suited to stellar population studies that seek to investigate potential shortcomings of contemporary
Galaxy models.
Subject headings: stars: fundamental parameters — stars: oscillations — stars: interiors
1. INTRODUCTION
The study of red giant stars has arguably been one
of the greatest success stories of NASA’s Kepler mission
(e.g., Garc´ıa & Stello 2015, and references herein). However, a failure of the second of four momentum wheels ended
the mission in 2013 because the spacecraft could no longer
acquire stable pointing towards its original field of view. Fortunately, ingenious use of the remaining spacecraft capabili1 Sydney Institute for Astronomy (SIfA), School of Physics, University of
Sydney, NSW 2006, Australia
2 Stellar Astrophysics Centre, Department of Physics and Astronomy,
Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
3 SETI Institute, 189 Bernardo Avenue, Mountain View, CA 94043, USA
4 Department of Astronomy, The Ohio State University, Columbus, OH
43210, USA
5 Department of Chemistry and Physics, Florida Gulf Coast University,
Fort Myers, FL 33965, USA
6 School of Physics & Astronomy, University of Birmingham, Edgbaston,
Birmingham, B15 2TT, UK
7 Department of Astronomy, Yale University, P.O. Box 208101, New
Haven, CT 06520-8101
8 Research School of Astronomy & Astrophysics, Mount Stromlo Observatory, The Australian National University, ACT 2611, Australia
9 Laboratoire AIM, CEA/DSM – CNRS - Univ.
Paris Diderot –
IRFU/SAp, Centre de Saclay, 91191 Gif-sur-Yvette Cedex, France
10 Space Science Institute, 4750 Walnut street Suite 205 Boulder, CO
80301 USA
11 INAF, IAPS Istituto di Astrofisica e Planetologia Spaziali, Roma, Italy
12 LESIA, Observatoire de Paris, PSL Research University, CNRS, Universit´e Pierre et Marie Curie, Universit´e Paris Diderot, 92195 Meudon,
France cedex, France
13 Department of Astronomy and Astrophysics, The Pennsylvania State
University, University Park, PA 16802
14 Institute for Gravitation and the Cosmos, The Pennsylvania State University, University Park, PA 16802
15 Instituto de Ciencias del Espacio (ICE-CSIC/IEEC) Campus UAB, Carrer de Can Magrans, s/n 08193 Cerdanyola del Valls
16 Leibnitz Institute f¨
ur Astrophysics (AIP), Potsdam, Germany
ties by NASA and Ball Aerospace engineers rejuvenated the
mission as K2 – a mission capable of stable pointing at any
field along the ecliptic for up to approximately three months
per pointing (Howell et al. 2014). In this configuration, the
Kepler roll angle drifts due to a torque applied by solar radiation pressure, but this can be counteracted by thruster firings
every six hours to maintain the spacecraft pointing. The K2
mission has enabled a broad range of new science including
stellar clusters (Nardiello et al. 2015), planets around bright
cool stars (Crossfield et al. 2015; Sanchis-Ojeda et al. 2015;
Vanderburg et al. 2015; Montet et al. 2015), solar system objects (Szab´o et al. 2015), stellar activity (Ramsay & Doyle
2015), eclipsing binaries (Conroy et al. 2014), asteroseismology (Jeffery & Ramsay 2014; Lund et al. 2015; Chaplin
2015) and, in particular, asteroseismological studies of the
Galaxy.
The potential for asteroseismic investigations of large populations of red giants aimed at Galactic studies was recently demonstrated using data from CoRoT and Kepler
(Miglio et al. 2009; Chaplin et al. 2011; Miglio et al. 2013;
Casagrande 2015). However, the scope of these early studies
was limited for two reasons: the small number of distinct direction in the Galaxy probed by those missions, and the highly
complex (and, at some level, not fully documented) selection
function of the observed red giants (Sharma et al. in preparation). With K2’s 360-degree coverage of the ecliptic the
collated efforts from the K2 observing campaigns, provide a
unique opportunity to probe different regions of the Galaxy,
including the thin and thick disks, the halo, and the bulge,
based on a purpose-built selection approach suitable for population studies.
In this Letter, we present initial results from the K2 Campaign 1 data. Based on a sample of red giants specifically
selected to study stellar populations on a galactic scale, our
Toyz: A Framework for Scientific Analysis of Large Datasets and Astronomical Images
Fred Moolekamp and Eric Mamajek
Department of Physics & Astronomy, University of Rochester, Rochester, NY, 14627-0171, USA
arXiv:1506.08930v1 [astro-ph.IM] 30 Jun 2015
Abstract
As the size of images and data products derived from astronomical data continues to increase, new tools are needed to visualize
and interact with that data in a meaningful way. Motivated by our own astronomical images taken with the Dark Energy Camera
(DECam) we present Toyz, an open source Python package for viewing and analyzing images and data stored on a remote server
or cluster. Users connect to the Toyz web application via a web browser, making it an convenient tool for students to visualize and
interact with astronomical data without having to install any software on their local machines. In addition it provides researchers
with an easy-to-use tool that allows them to browse the files on a server and quickly view very large images (> 2 Gb) taken with
DECam and other cameras with a large FOV and create their own visualization tools that can be added on as extensions to the
default Toyz framework.
Keywords: Big Data, Visualization, Python, HTML5, Web application
1. Introduction
In the past, large scientific datasets were used mainly by
large collaborations while independent researchers worked with
much more manageable volumes of data. Over the past few
years we’ve been entering a new paradigm where very large sets
of data are available to (and at times even generated by) much
smaller groups. This abundance of data has highlighted a shortage of scientific tools to store, organize, analyze, and visualize
that data. Fortunately this problem overlaps with the needs of
the industrial community at large and in the past decade there
has been a lot of work by traditional scientists, data scientists,
and software engineers to develop software to aid researchers
in dealing with this new (and rewarding) problem.
Unfortunately much of the current work in astronomy is often on the fringe of what is possible and has been done before,
meaning the types of data we work with poses new challenges,
which in turn create a need for new tools (Merenyi, 2014; Gopu
et al., 2014; Lins et al., 2013; Loebman et al., 2014; Federl
et al., 2012, 2011). Ideally these new tools should be built
on existing frameworks that are under active development by
software engineers to minimize the effort from research scientists while taking advantage of the latest technologies and updates to existing codes. The Python language has become a
fertile ground for rapid software development and with the creation of a vast array of modules for scientific image and data
processing like numpy (Walt et al., 2011), scipy (Jones et al.,
2001), pandas (McKinney, 2010) and scikit-image (van der
Walt et al., 2014); machine learning modules like scikit-learn
(Pedregosa et al., 2011); statistics and modeling packages like
scikits-statsmodels, pymc and emcee (Foreman-Mackey et al.,
2013), and what has become the de facto astronomy python
project astropy (Astropy Collaboration et al., 2013) and its affiliated packages.
Preprint submitted to Astronomy and Computing
While many of the tools listed above are useful for astronomers, data scientists, and software engineers; there is a
great divergence when it comes to tools for visualization. Much
of the interactivity and visualization work done in the realm of
data science and software development tends to be focused on
web frameworks like jQuery Ui, Highcharts, D3.js and even
more advanced libraries using webGL like PhiloGL, pathGL
and many others; or R libraries like ggplot2 (Wickham, 2009).
Contrast this with astronomy where programs like ds9 (Joye
and Mandel, 2003) that are used primarily by astronomers with
few updates and changes over the past decade. Several recent
python packages have been created to help bridge the gap between professional visualization tools and those available in astronomy: GLUE (Beaumont et al., 2014) provides a rich GUI
for interacting with data sets and images and Ginga is one of
the most advanced frameworks for viewing and interacting with
FITS images.
The disadvantage of using any of the visualization tools in
astronomy mentioned above is that to run efficiently all of them
must be run on a local machine with data stored locally. With
new instruments like the Dark Energy Camera (DECam) that
create 2Gb images ( .5Gb compressed) and over 1Tb of data
products per night (Valdes et al., 2014; Flaugher et al., 2012),
it’s no longer feasible to store an entire observing run (or even
a single night) on a laptop or PC. Recognizing the need for
a server side image viewer several groups have been independently developing web applications to serve images from a remote server to a client with only a web browser installed including VisiOmatic (Bertin et al., 2015), Data Labs (Fitzpatrick
et al., 2014), and now Toyz. VisiOmatic is an open source web
application running on an Apache web server with an IIPImage
(Pillay, 2014) server to display large images in a browser using a so called “slippy map” implementation (similar to Google
July 1, 2015
Realistic modeling of local dynamo processes on the Sun
I. N. Kitiashvili1 , A. G. Kosovichev2 , N. N. Mansour1 , A. A. Wray1
1
NASA Ames Research Center, Moffett Field, Mountain View, CA 94035, USA
arXiv:1506.08924v1 [astro-ph.SR] 30 Jun 2015
2
New Jersey Institute of Technology, Newark, NJ 07102, USA
ABSTRACT
Magnetic fields are usually observed in the quiet Sun as small-scale elements
that cover the entire solar surface (the ‘salt and pepper’ patterns in line-of-sight
magnetograms). By using 3D radiative MHD numerical simulations we find that
these fields result from a local dynamo action in the top layers of the convection
zone, where extremely weak ‘seed’ magnetic fields (e.g., from a 10−6 G) can
locally grow above the mean equipartition field, to a stronger than 2000 G field
localized in magnetic structures. Our results reveal that the magnetic flux is
predominantly generated in regions of small-scale helical downflows. We find
that the local dynamo action takes place mostly in a shallow, about 500 km deep,
subsurface layer, from which the generated field is transported into the deeper
layers by convective downdrafts. We demonstrate that the observed dominance
of vertical magnetic fields at the photosphere and horizontal fields above the
photosphere can be explained by small-scale magnetic loops produced by the
dynamo. Such small-scale loops play an important role in the structure and
dynamics of the solar atmosphere and that their detection in observations is
critical for understanding the local dynamo action on the Sun.
Subject headings: Sun: photosphere, chromosphere, magnetic fields; Methods:
numerical; MHD, plasmas, dynamo, turbulence
1.
Introduction
The origin of magnetic field generation is a key problem for understanding solar variability across a wide range of scales. Modern high-resolution observations of global magnetic
fields by the Helioseismic and Magnetic Imager (HMI) on NASA’s Solar Dynamics Observatory (SDO) (Scherrer et al. 2012), as well as investigations of small-scale magnetic fields in
1
e-mail: [email protected]
arXiv:1506.08902v1 [astro-ph.SR] 29 Jun 2015
Modeling the Complete Lightcurve of ω CMa
M. R. Ghoreyshi 1 , A. C. Carciofi1 , L. R. Rímulo1 , S. Otero2 , D. Baade3 , J. E.
Bjorkman4 , A. T. Okazaki5 , and Th. Rivinius6
1 Instituto
de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de
São Paulo, Rua do Matão 1226, São Paulo, SP 05508-900, Brazil;
[email protected] usp.br
2 American
Association of Variable Star Observers (AAVSO), Cambdrige, MA,
USA;
3 European
Organisation for Astronomical Research in the Southern
Hemisphere, Karl-Schwarzschild-Str. 2, 85748 Garching bei München,
Germany;
4 EDepartment
of Physics Astronomy, University of Toledo, MS111 2801 West
Bancroft Street, Toledo, OH 43606, USA;
5 Faculty
of Engineering, Hokkai-Gakuen University, Toyohira-ku, Sapporo
062-8605, Japan;
European Organisation for Astronomical Research in the Southern
Hemisphere, Santiago 19, Casilla 19001, Chile
Abstract. We have used the radiative transfer code HDUST to analyze and interpret
the long-term photometric behavior of the Be star ω CMa, considering four complete
cycles of disk formation and dissipation. This is the first time in which a full lightcurve
of a Be star was investigated and modeled including both disk build-up and dissipation
phases. Based on the quite good fit of the observed data we were able to derive the
history of stellar mass decretion rates (including long- and short-term changes) during
the disk formation and dissipation phases in all four cycles.
1.
Introduction
ω (28) CMa (HD 56139, HR2749; B3Ve) is one of the most observed southern Be
stars. Long-term photometric monitoring exhibits a quasi-regular cyclic variation with
an amplitude of about 0.m 5 in the V-Band. This allows to study evolution of the disk in
detail. In each cycle a new disk is formed during 2-3 years, and then dissipated in 5-6
years.
Carciofi et al. (2012) used ω CMa to model, for the first time, the light curve of a
Be star based on the viscous decretion disk (VDD) model (the theoretical description of
the model is given by Haubois et al. 2012). The model of the dissipation curve allowed
the authors to determine that the viscosity parameter of Shakura-Sunyaev (Shakura &
Sunyaev, 1973) is α = 1.0 ± 0.2. Such value for α suggests that viscosity may be
1
APCTP-Pre2015-018
arXiv:1506.08894v1 [astro-ph.CO] 29 Jun 2015
Towards general patterns of features
in multi-field inflation
Xian Gaoa and Jinn-Ouk Gongb,c
a Department
b Asia
of Physics, Tokyo Institute of Technology, Tokyo 152-8551, Japan
Pacific Center for Theoretical Physics, Pohang 790-784, Korea
c Department of Physics, Postech, Pohang 790-784, Korea
Abstract
We investigate the consequences of general curved trajectories in multi-field inflation.
After setting up a completely general formalism using the mass basis, which naturally
accommodates the notion of light and heavy modes, we study in detail the simple case
of two successive turns in two-field system. We find the power spectrum of the curvature
perturbation receives corrections that exhibit oscillatory features sinusoidal in the logarithm of the comoving wavenumber without slow-roll suppression. We show that this is
because of the resonance of the heavy modes inside and outside the mass horizon.
Draft version July 1, 2015
Preprint typeset using LATEX style emulateapj v. 5/2/11
A HIGH-RESOLUTION MULTIBAND SURVEY OF WESTERLUND 2 WITH THE HUBBLE SPACE
TELESCOPE I: IS THE MASSIVE STAR CLUSTER DOUBLE?
Peter Zeidler1,2 , Elena Sabbi2 , Antonella Nota2,3 , Eva K. Grebel1 , Monica Tosi5 , Alceste Z. Bonanos4 , Anna
Pasquali1 , Carol Christian2 , Selma E. de Mink6 , Leonardo Ubeda2
arXiv:1506.08887v1 [astro-ph.SR] 29 Jun 2015
Draft version July 1, 2015
ABSTRACT
We present first results from a high resolution multi-band survey of the Westerlund 2 region with
the Hubble Space Telescope. Specifically, we imaged Westerlund 2 with the Advanced Camera for
Surveys through the F 555W , F 814W , and F 658N filters and with the Wide Field Camera 3 in the
F 125W , F 160W , and F 128N filters. We derive the first high resolution pixel-to-pixel map of the
color excess E(B − V )g of the gas associated with the cluster, combining the Hα (F 658N ) and Paβ
(F 128N ) line observations. We demonstrate that, as expected, the region is affected by significant
differential reddening with a median of E(B − V )g = 1.87 mag. After separating the populations
of cluster members and foreground contaminants using a (F 814W − F 160W ) vs. F 814W colormagnitude diagram, we identify a pronounced pre-main-sequence population in Westerlund 2 showing
a distinct turn-on. After dereddening each star of Westerlund 2 individually in the color-magnitude
diagram we find via over-plotting PARSEC isochrones that the distance is in good agreement with
the literature value of ∼ 4.16 ± 0.33 kpc. With zero-age-main-sequence fitting to two-color-diagrams,
we derive a value of total to selective extinction of RV = 3.95 ± 0.135. A spatial density map of the
stellar content reveals that the cluster might be composed of two clumps. We estimate the same age
of 0.5–2.0 Myr for both clumps. While the two clumps appear to be coeval, the northern clump shows
a ∼ 20% lower stellar surface density.
Subject headings: techniques: photometric - stars: early type - stars: pre-main sequence - HII regions
- open clusters and associations: individual (Westerlund 2) - infrared: stars
1. INTRODUCTION
4
With a stellar mass of M ≥ 10 M⊙ (Ascenso et al.
2007) and an estimated molecular cloud mass of (1.7 ±
0.8 – 7.5) × 105 M⊙ (Furukawa et al. 2009; Dame
2007, both based on millimeter CO spectroscopy), the
young, massive star cluster Westerlund 2 (hereafter Wd2;
Westerlund 1961) is one of the most massive young
star clusters known in the Milky Way (MW). It is
embedded in the H II region RCW 49 (Rodgers et al.
1960) and located in the Carina-Sagittarius spiral arm
(α, δ) = (10h 23m 58s .1, −57◦45′ 49′′ )(J2000), (l, b) =
(284.3◦, −0.34◦ ). Moffat et al. (1991a) suggest that Wd2
contains more than 80 O-type stars.
Very few young (< 5 Myr) and massive (> 104 M⊙ )
star clusters are known in the MW, but they are
frequently observed in the Magellanic Clouds (e.g.,
Gascoigne & Kron 1952; Clark et al. 2005) as well as in
the more distant Universe, especially in disk and starburst galaxies (e.g., Hodge 1961). Therefore, Wd2 is a
perfect target to study the star formation process and
feedback of the gas in the presence of massive stars as
1 Astronomisches Rechen-Institut, Zentrum f¨
ur Astronomie
der Universit¨
at Heidelberg, M¨
onchhofstr. 12-14, 69120 Heidelberg, Germany [email protected]
2 Space Telescope Science Institute, 3700 San Martin Drive,
Baltimore, MD 21218, USA
3 ESA, SRE Operations Devision
4 IAASARS, National Observatory of Athens, GR-15326 Penteli, Greece
5 INAF - Osservatorio Astronomico di Bologna
6 Astronomical Institute Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam, The Netherlands
well as the possible triggering of star formation in the surrounding molecular cloud (suggested to occur in RCW 49
by Whitney et al. 2004; Churchwell et al. 2004, using
Spitzer mid-IR images). In fact, many globular clusters
are less massive than Wd2 (see, e.g., Misgeld & Hilker
2011).
The Wd2 cluster has been widely discussed in the literature in the last decade, yet its physical properties
are poorly known. There is a considerable disagreement
about the distance of Wd2, ranging from values of 2.8 kpc
(Rauw et al. 2007; Ascenso et al. 2007; Carraro et al.
´
2013), 4.16 kpc (Vargas Alvarez
et al. 2013), 5.7 kpc
(Piatti et al. 1998), 6.4 kpc (Carraro & Munari 2004) to
even 8 kpc (Rauw et al. 2007, 2011). A consensus has not
been reached on the age of Wd2 either, although there
seems to be general agreement that the cluster as a whole
is younger than 3 Myr and that the core may be even
younger than 2 Myr (Ascenso et al. 2007; Carraro et al.
2013). This young age combined with the cluster halflight radius of about 2.4 pc and its total mass make it
likely that Wd2 is younger than half of its typical crossing
time (∼ 5.5 Myr Gieles & Portegies Zwart 2011). Therefore, the physical conditions of Wd2 are very close to its
initial conditions.
Over the last years a series of spectroscopic observations of the most massive stars was performed.
Moffat et al. (1991b) used U BV photometry and low
resolution spectroscopy in order to classify six O-stars
within Wd2 as O6–7 V objects and to obtain a distance
of d = 7.9+1.2
−1.0 kpc, while Piatti et al. (1998) reanalyzed a
subset of O stars from (Moffat et al. 1991b) to determine
a distance of d = 5.7 ± 0.3 kpc. Two snapshot spectra of
Draft version July 1, 2015
Preprint typeset using LATEX style emulateapj v. 5/2/11
DATA REDUCTION WITH THE MIKE SPECTROMETER
Rebecca M. Bernstein1 , Scott M. Burles2 , J. Xavier Prochaska3
arXiv:1506.08864v1 [astro-ph.IM] 29 Jun 2015
Draft version July 1, 2015
ABSTRACT
This manuscript describes the design, usage, and data-reduction pipeline developed for the Magellan Inamori Kyocera Echelle (MIKE) spectrometer used with the Magellan telescope at the Las
Campanas Observatory. We summarize the basic characteristics of the instrument and discuss observational procedures recommended for calibrating the standard data products. We detail the design
and implementation of an IDL based data-reduction pipeline for MIKE data (since generalized to
other echelle spectrometers, e.g. Keck/HIRES, VLT/UVES). This includes novel techniques for flatfielding, wavelength calibration, and the extraction of echelle spectroscopy. Sufficient detail is provided
in this manuscript to enable inexperienced observers to understand the strengths and weaknesses of
the instrument and software package and an assessment of the related systematics.
Subject headings: instrumentation : spectrographs – methods: data analysis – techniques: spectroscopic
1. INTRODUCTION
The field of astronomy has witnessed rapid growth
over the past few decades leading to the division of astronomers into observers, instrumentationalists, and theorists. In recent years, there is even an increased specialization within these sub-classes (e.g. numericists vs.
semi-analytic theorists, spectroscopy vs. adaptive optics
imaging). Similarly, as observatories approach billion
dollar projects the complexity of building a facility-class
instruments exceeds the capacity of a single astronomer.
In contrast to the recent past, it is impractical for the
majority of observational astronomers to design and fabricate a new instrument as the most efficient means of
pursuing his/her scientific interests.
Instead, modern observers now acquire and analyze
data-sets without having even visited the telescope or
even having developed intimate knowledge of the instrument. Furthermore, many observers now rely on data reduction pipelines to produce calibrated, science-quality
data without a comprehensive knowledge of the trade-offs
and limitations considered by the software designer(s).
Although this trend toward virtual observing may improve the efficiency with which new data is obtained and
analyzed, users of these tools are prone to having an incomplete understanding of his/her experiment.
Motivated by these trends, we have written the following paper to document the design, usage, and data
reduction pipeline of the MIKE echelle spectrometer
(Bernstein et al. 2003). We discuss observational techniques for the calibration of these data, new algorithms
to improve sky subtraction and flat fielding, and object
extraction. Although we focus on the MIKE spectrometer, we will give a pedagogical discussion that generalizes to the majority of echelle spectrometers in use today
and in the future (e.g. HIRES, UVES; Vogt et al. 1994;
1 Observatories of the Carnegie Institution for Science, 813
Santa Barbara Street, Pasadena, CA 91101, USA
2 Cutler Group, LP, 101 Montgomery St. #700, SF, CA 94104
3 Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz,
CA 95064, USA
Dekker et al. 2000). Portions of this manuscript also
generalize to many of the low dispersion spectrometers
in use today (e.g. DEIMOS, FORS, IMACS).
The principal goal of this paper is to describe the
data reduction pipeline designed for the MIKE spectrometer and then generalized to the HIRES4 , UVES
(e.g. Ellison, Prochaska & Lopez 2007) and ESI5 spectrometers within the XIDL package6 maintained by JXP.
Many of the techniques we have implemented follow
the standard lore of astronomical research, and we have
benefited from many previous works on this topic (e.g.
Churchill & Allen 1995; Kelson 2003). Furthermore, our
efforts have been inspired by (and take advantage of)
the algorithms developed for the spectral reductions of
the Sloan Digital Sky Survey (SDSS; Burles & Schlegel,
in prep.). Several unique characteristics of the MIKE
spectrometer (e.g. tilted sky lines), however, have inspired new techniques for wavelength calibration, flat
fielding, and object extraction. We describe these in detail in this manuscript; they may be of interest to future
instruments where similar issues arise (e.g. X-shooter;
D’Odorico et al. 2006).
The paper is organized as follows. In §2, we describe
the MIKE double echelle briefly and highlight points
which directly influence the design and implementation
of the reduction algorithms described in this paper. In
§3, we describe the layout of the software pipeline. In §4,
we describe the image processing algorithms. In §5, we
describe the flat field algorithms. In §6, we describe the
wavelength calibration algorithms. In §7, we describe object tracing and extraction. Finally, we describe fluxing
and coaddition algorithms in § 8.
2. DESCRIPTION OF THE INSTRUMENT
MIKE is a double echelle spectrograph which was designed for the Magellan telescopes and installed on Magellan II (Clay) during November 2002. The standard configuration for MIKE is set by the cross-over wavelength
4
5
6
http://www.ucolick.org/∼xavier/HIRedux
http://www2.keck.hawaii.edu/inst/esi/ESIRedux/
http://www.ucolick.org/∼xavier/IDL/index.html
Draft version July 1, 2015
Preprint typeset using LATEX style emulateapj v. 5/2/11
THE KECK + MAGELLAN SURVEY FOR LYMAN LIMIT ABSORPTION III: SAMPLE DEFINITION AND
COLUMN DENSITY MEASUREMENTS
J. Xavier Prochaska1 , John M. O’Meara2 , Michele Fumagalli3,4 , Rebecca A. Bernstein4 , Scott M. Burles6
arXiv:1506.08863v1 [astro-ph.CO] 29 Jun 2015
Draft version July 1, 2015
ABSTRACT
We present an absorption-line survey of optically thick gas clouds – Lyman Limit Systems (LLSs)
– observed at high dispersion with spectrometers on the Keck and Magellan telescopes. We measure
column densities of neutral hydrogen NHI and associated metal-line transitions for 157 LLSs at zLLS =
1.76 − 4.39 restricted to 1017.3 cm−2 ≤ NHI < 1020.3 cm−2 . An empirical analysis of ionic ratios
indicates an increasing ionization state of the gas with decreasing NHI and that the majority of LLSs
are highly ionized, confirming previous expectations. The Si+ /H0 ratio spans nearly four orders-ofmagnitude, implying a large dispersion in the gas metallicity. Fewer than 5% of these LLSs have no
positive detection of a metal transition; by z ∼ 3, nearly all gas that is dense enough to exhibit a very
high Lyman limit opacity has previously been polluted by heavy elements. We add new measurements
to the small subset of LLS (≈ 5 − 10%) that may have super-solar abundances. High Si+ /Fe+ ratios
suggest an α-enhanced medium whereas the Si+ /C+ ratios do not exhibit the super-solar enhancement
inferred previously for the Lyα forest.
Subject headings: absorption lines – intergalactic medium – Lyman limit systems
1. INTRODUCTION
As a packet of ionizing radiation (hν ≥ 1 Ryd) traverses the universe, it has a high probability of encountering a slab of optically thick, H I gas. For sources in
the z ∼ 4 universe the mean free path is only ≈ 30 Mpc
(physical; Worseck et al. 2014), i.e. less than 2% of the
event horizon. Observationally, researchers refer to this
optically thick gas as Lyman limit systems (LLSs) owing
to their unmistakable signature of continuum opacity at
the Lyman limit (≈ 912˚
A) in the system restframe. A
fraction of this gas lies within the dense, neutral interstellar medium (ISM) of galaxies, yet the majority of opacity must arise from gas outside the ISM (e.g. Fumagalli
et al. 2011b; Ribaudo et al. 2011). Indeed, the interplay
between galaxies and the LLS is a highly active area of
research which includes studies of the so-called circumgalactic medium (CGM; e.g. Steidel et al. 2010; Werk
et al. 2013; Prochaska et al. 2014a).
For many decades, LLS have been surveyed in quasar
spectra (e.g. Tytler 1982; Sargent et al. 1989; StorrieLombardi et al. 1994), albeit often from heterogeneous
samples. These works established the high incidence
of LLSs which evolves rapidly with redshift. With the
realization of massive spectral datasets, a renaissance
of LLS surveys has followed yielding statistically robust measurements from homogenous and well-selected
quasar samples (Prochaska et al. 2010; Songaila & Cowie
1 Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz,
CA 95064, USA
2 Department of Chemistry and Physics, Saint Michael’s College. One Winooski Park, Colchester, VT 05439, USA
3 Institute for Computational Cosmology, Department of
Physics, Durham University, South Road, Durham, DH1 3LE,
UK
4 Observatories of the Carnegie Institution for Science, 813
Santa Barbara Street, Pasadena, CA 91101, USA
6 Cutler Group, LP., 101 Montgomery St., San Francisco, CA
94104, USA
2010; Ribaudo et al. 2011; O’Meara et al. 2013; Fumagalli et al. 2013). Analysis of these hundreds of systems
reveals an incidence of approximately 1.2 systems per
unit redshift at z ∼ 3 that evolves steeply with redshift
`(z) ∝ (1+z)1.5 for z ≈ 1−5 (Ribaudo et al. 2011; Fumagalli et al. 2013). With these same spectra, researchers
have further measured the mean free path of ionizing radiation (λ912
mfp ; Prochaska et al. 2009; O’Meara et al. 2013;
Fumagalli et al. 2013; Worseck et al. 2014), which sets the
intensity and shape of the extragalactic UV background.
Following the redshift evolution of the LLS incidence,
λ912
mfp also evolves steeply with the expanding universe,
implying a more highly ionized universe with advancing
cosmic time (Worseck et al. 2014).
The preponderance of LLSs bespeaks a major reservoir
of baryons. In particular, given the apparent paucity of
heavy elements within galaxies (e.g. Bouch´e et al. 2006;
Peeples et al. 2014), the LLSs may present the dominant
reservoir of metals in the universe (e.g. Prochaska et al.
2006). However, a precise calculation of the heavy elements within LLSs and their contribution to the cosmic
budget has not yet been achieved. Despite our success at
surveying hundreds of LLSs, there have been few studies
resolving their physical properties and these have generally examined a few individual cases (e.g. Steidel 1990;
Prochaska 1999) or composite spectra (Fumagalli et al.
2013). This reflects both the challenges related to data
acquisition and analysis together with a historical focus
in the community towards the ISM of galaxies (probed by
DLAs) and the more diffuse intergalactic medium (IGM).
At z > 2, a few works have examined the set of LLSs
with high H I column density (NHI ≥ 1019 cm−2 ), generally termed the super-LLSs or sub-damped Lyα systems.
Their NHI frequency distribution f (NHI , X) and chemical abundances have been analyzed from a modestly sized
sample (Dessauges-Zavadsky et al. 2003; P´eroux et al.
2005; O’Meara et al. 2007; Zafar et al. 2013; Som et al.
2013). Ignoring ionization corrections, which may not
Published in Phys. Rev. D 91, 104023 (2015): http://journals.aps.org/prd/abstract/10.1103/PhysRevD.91.104023.
Copyright 2015 American Physical Society
Corrected constraints on big bang nucleosynthesis in a modified gravity model of
f (R) ∝ Rn
Motohiko Kusakabe1,2 ,∗ Seoktae Koh3 , K. S. Kim1 , and Myung-Ki Cheoun2
arXiv:1506.08859v1 [astro-ph.CO] 29 Jun 2015
1
School of Liberal Arts and Science, Korea Aerospace University, Goyang 412-791, Korea
2
Department of Physics, Soongsil University, Seoul 156-743, Korea and
3
Department of Science Education, Jeju National University, Jeju 690-756, Korea
(Dated: July 1, 2015)
Big bang nucleosynthesis in a modified gravity model of f (R) ∝ Rn is investigated. The only
free parameter of the model
√ is a power-law index n. We find cosmological solutions in a parameter
region of 1 < n ≤ (4 + 6)/5. We calculate abundances of 4 He, D, 3 He, 7 Li, and 6 Li during big
bang nucleosynthesis. We compare the results with the latest observational data. It is then found
that the power-law index is constrained to be (n − 1) = (−0.86 ± 1.19) × 10−4 (95 % C.L.) mainly
from observations of deuterium abundance as well as 4 He abundance.
PACS numbers: 26.35.+c, 04.50.Kd, 98.80.Es, 98.80.Ft
I.
INTRODUCTION
The present standard cosmological model is based
on Einstein’s general relativity with the FriedmannLemaître-Robertson-Walker metric for a homogeneous
and isotropic universe. All elementary particles of the
standard particle model and dark matter and dark energy are taken into account in the cosmological model.
The standard cosmological model has been supported
by various kinds of astronomical observations. Observations of light element abundances in old astronomical
objects are, however, one of the most important premises
of the standard cosmological model. Roughly speaking,
the theoretical predictions of light element abundances
are consistent with observational data. In modified gravitational theories, cosmic expansion histories are different
from that in the standard model, while in modified particle theories additional effects of exotic particles operate
in the early universe. As a result, primordial elemental abundances in these models are different from those
in the standard big bang nucleosynthesis (BBN) model.
Therefore, we can limit any models which predict changes
in abundances.
The baryogenesis in a modified gravity model of
f (R) ∝ Rn , where R is the Ricci scalar and n is the
power-law index, has been studied to explain the small
baryon-to-photon number ratio of the Universe [1]. The
authors derived a cosmological solution in which the scale
factor of the universe scales as a(t) ∝ tα , where t is the
cosmic
√ time and α is a real parameter. They argued that
(4 − 6)/5 ≤ n ≤ 1 should be satisfied in order to realize a positive temperature of the universe. The BBN
in the same model has also been analytically studied [2].
They constrained the index to be 1 − n . 2 × 10−4 by a
comparison of an analytical estimation of 4 He abundance
and observational data.
In this paper, we calculate BBN in the model of
∗ Electronic
address: [email protected]
f (R) ∝ Rn with a detailed nuclear reaction network
code and show abundances of all light elements produced
during BBN. In Ref. [2], only 4 He abundance has been
studied semianalytically. In this paper, however, it is
found that observational constraints on the primordial
D abundance can limit the modified gravity model more
stringently than those on the 4 He abundance. On the
other hand, limits derived from observations of 3 He, 7 Li,
and 6 Li abundances are less stringent than those of D
and 4 He. In addition, we point out that models of f (R)
should describe the accelerated expansion of the present
Universe. We find that the model used in the previous
study [1, 2] is excluded by this requirement, and we suggest a simple correction to the model. In this paper, we
consider three models: (1) a new model which describes
the accelerated expansion of the present Universe, (2) the
previous model [1, 2] which cannot describe the expansion, and (3) a corrected version of (2) which describes
the expansion. Although the limit on the f (R) ∝ Rn
model is corrected, our revised result supports the previous conclusion that the consideration of BBN excludes
parameter values of n largely different from unity [2].
In Sec. II, the modified gravity model is introduced,
and equations for the cosmic evolution are derived. In
Sec. III, our code for the BBN calculation is briefly explained. In Sec. IV, observational constraints on the
primordial light element abundances are described. In
Sec. V, a result of BBN is shown and interpreted. In
Sec. VI, this work is briefly summarized.
II.
COSMOLOGY OF f (R) ∝ Rn GRAVITY
In this section, formulas of the cosmology in the modified gravity model are shown. First, we derive equations
of motion. The action is given by
Z
√
1
S = 2 d4 x −gf (R) + Sm (gµν , φm ),
(1)
2κ
where κ2 = 8πG is defined, with G Newton’s constant,
gµν the metric tensor, g the determinant of the metric
Design and Early Development of a UAV Terminal
and a Ground Station for Laser Communications
Alberto Carrasco-Casado*, Ricardo Vergaz, José M. Sánchez-Pena
Dpto. Tecnología Electrónica, Universidad Carlos III de Madrid
Avda. Universidad, 30, 28911, Madrid, Spain;
Published in SPIE Proceedings Vol. 8184, 29 September 2011, DOI: 10.1117/12.898216
ABSTRACT
A free-space laser communication system has been designed and partially developed as an alternative to standard RF
links from UAV to ground stations. This project belongs to the SINTONIA program (acronym in Spanish for low
environmental-impact unmanned systems), led by BR&TE (Boeing Research and Technology Europe) with the purpose
of boosting Spanish UAV technology.
A MEMS-based modulating retroreflector has been proposed as a communication terminal onboard the UAV, allowing
both the laser transmitter and the acquisition, tracking and pointing subsystems to be eliminated. This results in an
important reduction of power, size and weight, moving the burden to the ground station. In the ground station, the ATP
subsystem is based on a GPS-aided two-axis gimbal for tracking and coarse pointing, and a fast steering mirror for fine
pointing. A beacon-based system has been designed, taking advantage of the retroreflector optical principle, in order to
determine the position of the UAV in real-time. The system manages the laser power in an optimal way, based on a
distance-dependent beam-divergence control and by creating two different optical paths within the same physical path
using different states of polarization.
Keywords: Free-space optical communications, free-space lasercom, UAV communications, modulating retroreflector,
retromodulator, MEMS modulator, acquisition, tracking and pointing.
1. INTRODUCTION
A free-space optical communication system has been designed and partially developed as an alternative to standard radio
frequency (RF) links from Unmanned Aerial Vehicles (UAV) to ground stations. This project belongs to the SINTONIA
[1] program (acronym in Spanish for low-environmental-impact unmanned systems), led by BR&TE (Boeing Research
and Technology Europe) with the purpose of boosting Spanish UAV technology. The work of GDAF-UC3M is under the
coordination of INDRA, S.A. and INSA, S.A. companies.
Small UAVs are becoming a key part of national security and it is foreseen that in the future this tendency will continue
with a stronger and stronger impact. A great flexibility has been demonstrated by these kinds of aircraft, which have
been used in a big number of both civil and military objectives and scenarios, from agriculture to meteorology and from
research to military warfare. The US Army alone holds over 4,000 UAVs with many more programmed [2].
Communications play a more important role in the operation of unmanned aircraft than they do in manned ones because
all the decision-making occurs on the ground, either before or during the flight itself. Currently, telecommunications
links between UAVs and ground stations are based on RF systems and low-earth-orbiting satellites [3]. Both are long
range communications but also have low bit rates, usually in the order of hundreds of kbps or less, and in the case of
satellite communications the payload involves an important burden regarding to mass and weight onboard.
The move to optical carrier frequencies involves a qualitative leap because it provides a shift of several orders of
magnitude, from MHz to hundreds of thousands of GHz. Since the minimum divergence, given by the diffraction limit of
an aperture, is dependent on the wavelength of the electromagnetic wave [4], this shift implies also a dramatic decrease
*[email protected]
Draft version July 1, 2015
Preprint typeset using LATEX style emulateapj v. 05/12/14
arXiv:1506.08850v1 [astro-ph.EP] 29 Jun 2015
OGLE-2012-BLG-0563LB: A SATURN-MASS PLANET AROUND AN M DWARF WITH THE MASS
CONSTRAINED BY SUBARU AO IMAGING
A. FukuiM 1,M , A. GouldU 1,U , T. SumiM 2,M , D. P. BennettM 3,M , I. A. BondM 4,M , C. HanU 2,U , D. SuzukiM 3,M ,
J.-P. BeaulieuP 1,P , V. BatistaP 1,U,P , A. UdalskiO1,O , R. A. StreetR1,R , Y. TsaprasR1,R2,R3,R , M.
HundertmarkR6,R7,R ,
and
F. AbeM 5 , M. FreemanM 6 , Y. ItowM 5 , C. H. LingM 4 , N. KoshimotoM 2 , K. MasudaM 5 , Y. MatsubaraM 5 ,
Y. MurakiM 5 , K. OhnishiM 8 , L. C. PhilpottM 9 , N. RattenburyM 6 , T. SaitoM 10 , D. J. SullivanM 7 ,
M 11
P. J. Tristram
, A. YoneharaM 12
(The MOA Collaboration),
J.-Y. ChoiU 2 , G.W. ChristieU 3 , D.L. DePoyU 4 , Subo DongU 5 , J. DrummondU 6 , B.S. GaudiU 1 , K.-H. HwangU 2 ,
A. KavkaU 1 , C.-U. LeeU 7 , J. McCormickU 8 , T. NatuschU 3,U 9 , H. NganU 3 , H. ParkU 2 , R.W. PoggeU 1 , I-G. ShinU 2 ,
T.-G. TanU 10 , J.C. YeeU 1,U 11,U 12
(The µFUN Collaboration)
M. K. Szyma´
nskiO1, G. Pietrzy´
nskiO1 , I. Soszy´
nskiO1 , R. PoleskiO1,U 1 , S. KozlowskiO1 , P. PietrukowiczO1 ,
K. UlaczykO1 , L. WyrzykowskiO1
(The OGLE Collaboration),
D. M. BramichR4 , P. BrowneR5 , M. DominikR5,† , K. HorneR5 , S. IpatovR8,R9 , N. KainsR10,R11 , C. SnodgrassR12,R13 ,
I. A. SteeleR14
(The RoboNet Collaboration)
M1
Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, Asakuchi, 719-0232 Okayama, Japan
Dept. of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, 560-0043
Osaka, Japan
M 3 Dept. of Physics, University of Notre Dame, Notre Dame, IN 46556, USA
M 4 Institute of Information and Mathematical Sciences, Massey University, Private Bag 102-904, North Shore Mail Centre, Auckland,
New Zealand
M 5 Solar-Terrestrial Environment Laboratory, Nagoya University, 464-8601 Nagoya, Japan
M 6 Dept. of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand
M 7 School of Chemical and Physical Sciences, Victoria University, Wellington, New Zealand
M 8 Nagano National College of Technology, 381-8550 Nagano, Japan
M 9 Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia, V6T 1Z4,
Canada
M 10 Tokyo Metropolitan College of Industrial Technology, 116-8523 Tokyo, Japan
M 11 Mt. John University Observatory, P.O. Box 56, Lake Tekapo 8770, New Zealand
M 12 Department of Physics, Faculty of Science, Kyoto Sangyo University, Motoyama, Kamigamo, Kita-Ku, Kyoto, Kyoto 603-8555,
Japan
U 1 Department of Astronomy, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA; [email protected]
U 2 Department of Physics, Institute for Astrophysics, Chungbuk National University, 371-763 Cheongju, Korea
U 3 Auckland Observatory, Auckland, New Zealand; [email protected]
U 4 Dept. of Physics, Texas A&M University, College Station, TX, USA; [email protected]
U 5 Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Road 5, Hai Dian District, Beijing 100871, China
U 6 Possum Observatory, Patutahi, New Zealand
U 7 Korea Astronomy and Space Science Institute, 305-348 Daejeon, Korea
U 8 Farm Cove Observatory, Centre for Backyard Astrophysics, Pakuranga, Auckland, New Zealand; [email protected]
U 9 AUT University, Auckland, New Zealand; [email protected]
U 10 Perth Exoplanet Survey Telescope, Perth, Australia
U 11 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
U 12 Sagan Fellow
O1 Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
P 1 Institut d’Astrophysique de Paris, Universit’e Pierre et Marie Curie, CNRS UMR7095, 98bis Boulevard Arago, 75014 Paris, France
R1 Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, suite 102, Goleta, CA 93117, USA
R2 Astronomisches Rechen-Institut, Zentrum f¨
ur Astronomie der Universit¨
at Heidelberg (ZAH), 69120 Heidelberg, Germany
R3 School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS, UK
R4 Qatar Environment and Energy Research Institute, Qatar Foundation, P.O. Box 5825, Doha, Qatar
R5 SUPA, School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
R6 Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100, København Ø, Denmark
R7 Centre for Star and Planet Formation, Natural History Museum, University of Copenhagen, Østervoldgade 5-7, 1350, København K,
Denmark
R8 Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academy of Sciences, Kosygina 19, 119991, Moscow, Russia
R9 Space Research Institute of Russian Academy of Sciences, Profsoyuznaya st. 84/32, Moscow, Russia
R10 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei M¨
unchen, Germany
R11 Space Telescope Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
R12 Planetary and Space Sciences, Department of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK
R13 Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 G¨
ottingen, Germany
R14 Astrophysics Research Institute, Liverpool John Moores University, Liverpool L3 5RF, UK and
† Royal Society University Research Fellow
M2
2
Draft version July 1, 2015
ABSTRACT
We report the discovery of a microlensing exoplanet OGLE-2012-BLG-0563Lb with the planet-star
mass ratio of ∼ 1 × 10−3 . Intensive photometric observations of a high-magnification microlensing
event allow us to detect a clear signal of the planet. Although no parallax signal is detected in the
light curve, we instead succeed at detecting the flux from the host star in high-resolution JHK ′ -band
images obtained by the Subaru/AO188 and IRCS instruments, allowing us to constrain the absolute
physical parameters of the planetary system. With the help of a spectroscopic information of the
source star obtained during the high-magnification state by Bensby et al. (2013), we find that the
+0.12
lens system is located at 1.3 +0.6
−0.8 kpc from us, and consists of an M dwarf (0.34 −0.20 M⊙ ) orbited by
+0.26
a Saturn-mass planet (0.39 +0.14
−0.23 MJup ) at the projected separation of 0.74 −0.42 AU (close model) or
4.3 +1.5
−2.5 AU (wide model). The probability of contamination in the host star’s flux, which would reduce
the masses by a factor of up to 3, is estimated to be 17 %. This possibility can be tested by future
high-resolution imaging. We also estimate the (J − Ks ) and (H − Ks ) colors of the host star, which are
marginally consistent with a low-metallicity mid-to-early M dwarf, although further observations are
required for the metallicity to be conclusive. This is the fifth sub-Jupiter-mass (0.2 < mp /MJup < 1)
microlensing planet around an M dwarf with the mass well constrained. The relatively rich harvest
of sub-Jupiters around M dwarfs is contrasted with a possible paucity of ∼1–2 Jupiter-mass planets
around the same type of star, which can be explained by the planetary formation process in the core
accretion scheme.
Keywords: planetary systems — planets and satellites: detection — planets and satellites: gaseous
planets — stars: late-type — techniques: high angular resolution — techniques: photometric
1. INTRODUCTION
Microlensing is a unique and powerful technique to
probe exoplanets with a wide range of masses just beyond the snow line, where gas-giant planets can efficiently form according to the core-accretion models (e.g.,
Pollack et al. 1996; Kokubo & Ida 2002). The planetarymass distribution probed by microlensing therefore provides a valuable information about the planetary formation process less affected by several post-formation effects
such as orbital migration and mass loss due to stellar
irradiation. In addition, microlensing is most sensitive
to exoplanets around M dwarfs including late-type ones,
which have not sufficiently been surveyed by other detection techniques due to the faintness of this type of star.
The core-accretion models predict that massive Jovian
planets are rare around low-mass stars due to the lack
of planet-forming materials (e.g., Ida & Lin 2005), which
can thus be tested by microlensing.
Thanks to a huge effort by microlensing surveys and
follow-up projects to date, the number of microlensing planets has reached 35 6 , among which ∼ 60% are
hosted by M dwarfs. These discoveries have revealed
that low-mass planets are much more abundant than
massive ones, in agreement with the core-accretion scenarios (Sumi et al. 2010; Gould et al. 2010; Cassan et al.
2012). On the other hand, super-Jupiter-mass planets
(& 2MJup) have also been discovered around M dwarfs
(e.g., Dong et al. 2009; Batista et al. 2011; Tsapras et al.
2014), which at the same time challenges the same sceM Microlensing Observations in Astrophysics (MOA) Collaboration.
U Microlensing Follow-up Network (µFUN) Collaboration.
O Optical Gravitational Lensing Experiment (OGLE) Collaboration.
P Probing Lensing Anomalies NETwork (PLANET) Collaboration.
R RoboNet Collaboration.
6 http://exoplanet.eu
narios.
However, the statistics of microlensing planets are not
yet high enough to draw a clear structure of the planetary
mass distribution, in terms of the number and accuracy.
In particular, about half of all planetary microlensing
events do not show parallax effects in the light curves,
without which one cannot measure the absolute masses
of the planet and host star from the light curve alone.
In such cases, the physical parameters of the planetary
system have often been estimated by the Bayesian technique, which uses Galactic-model priors (a stellar mass
function, stellar number density, and stellar velocity distribution) to draw posterior probability distributions of
the physical parameters. This technique could have a
meaning when the number of planets is statistically large
enough, however, the individual values are not accurate.
Furthermore, this technique relies on an assumption that
the planet occurrence probability is uniform for all stars
independent of stellar properties, such as stellar mass
and Galactic location, and therefore the results obtained
by this technique should be treated with caution.
Another method to constrain the physical parameters
of the lens system is detecting (or putting an upper
limit on) the emission from the host (lens) star by highresolution imaging. High resolution is essential to deblend unrelated stars and extract the lens+source composite flux. Although it is usually not possible to spatially resolve the lens star from the background source
star until a decade after the microlensing event for the
current facilities, even without resolving the two stars,
the lens star’s flux can be extracted by subtracting the
source star’s flux obtained by a light-curve analysis from
the lens+source composite flux. The extracted lens flux
provides a mass-distance relation of the host star, allowing us to solve for the mass and distance by combining
with another mass-distance relation provided by the angular Einstein radius θE , which can be derived in most
c ESO 2015
Astronomy & Astrophysics manuscript no. 24933
July 1, 2015
VLT X-shooter spectroscopy of the nearest brown dwarf binary⋆
N. Lodieu1,2 , M. R. Zapatero Osorio3 , R. Rebolo1,2,4 , V. J. S. B´ejar1,2 , Y. Pavlenko5,6 , A. P´erez-Garrido7
1
2
3
arXiv:1506.08848v1 [astro-ph.SR] 29 Jun 2015
4
5
6
7
Instituto de Astrof´ısica de Canarias (IAC), Calle V´ıa L´actea s/n, E-38200 La Laguna, Tenerife, Spain. e-mail:
nlodieu,vbejar,[email protected]
Departamento de Astrof´ısica, Universidad de La Laguna (ULL), E-38205 La Laguna, Tenerife, Spain.
Centro de Astrobiolog´ıa (CSIC-INTA), Ctra. Ajalvir km 4, E-28850 Torrej´on de Ardoz, Madrid, Spain. e-mail:
[email protected]
Consejo Superior de Investigaciones Cient´ıficas, CSIC, Spain.
Main Astronomical Observatory of the National Academy of Sciences of Ukraine.
Center for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB, UK
Universidad Polit´ecnica de Cartagena, Campus Muralla del Mar, Cartagena, E-30202 Murcia, Spain.
Received July 1, 2015; accepted July 1, 2015
ABSTRACT
Aims. The aim of the project is to characterise both components of the nearest brown dwarf sytem to the Sun, WISE
J104915.57−531906.1 (also proposed as Luhman 16AB) at optical and near-infrared wavelengths.
Methods. We obtained high signal-to-noise intermediate-resolution (R ∼ 6000–11000) optical (600–1000 nm) and near-infrared
(1000–2480nm) spectra of each component of Luhman 16AB, the closest brown dwarf binary to the Sun, with the X-Shooter instrument on the Very Large Telescope (VLT).
Results. We classify the primary and secondary of the Luhman 16 system as L6–L7.5 and T0±1, respectively, in agreement with
previous measurements published in the literature. We present measurements of the lithium pseudo-equivalent widths, which appears
of similar strength on both components (8.2±1.0Å and 8.4±1.5Å for the L and T components, respectively). The presence of lithium
(7 Li) in both components imply masses below 0.06 M⊙ while comparison with models suggests lower limits of 0.04 M⊙ . The detection
of lithium in the T component is the first of its kind. Similarly, we assess the strength of other alkali lines (e.g. pseudo-equivalent
widths of 6–7Å for RbI and 4–7Å for CsI) present in the optical and near-infrared regions and compare with estimates for L and
T dwarfs. We also derive effective temperatures and luminosities of each component of the binary: −4.66±0.08 dex and 1305+180
−135
for the L dwarf and −4.68±0.13 dex and 1320+185
−135 for the T dwarf, respectively. Using our radial velocity determinations, the binary
does not appear to belong to any of the well-known moving group. Our preliminary theoretical analysis of the optical and J-band
spectra indicates that the L- and T-type spectra can be reproduced with a single temperature and gravity but different relative chemical
abundances which impact strongly the spectral energy distribution of L/T transition objects.
Key words. Stars: brown dwarfs — techniques: spectroscopic
1. Introduction
Since the discovery of the first brown dwarfs in 1995
(Nakajima et al. 1995; Rebolo et al. 1995), the field of substellar research has made enormous progress with the discovery of more than 1000 nearby ultracool dwarfs, defined
as objects with spectral types later than M7, which include
L (∼1300–2200 K; Mart´ın et al. 1999; Kirkpatrick et al. 2000;
Basri et al. 2000; Leggett et al. 2000) and T dwarfs (∼1300–
600 K; Burgasser et al. 2006). The coolest brown dwarfs ever
found to date, originally nicknamed Y dwarfs (Kirkpatrick et al.
1999) have been announced by the Wide Infrared Survey
Explorer (WISE; Wright et al. 2010) team (Cushing et al. 2011;
Kirkpatrick et al. 2012; Tinney et al. 2012). They have temperatures estimated to 500–300 K and masses below 0.01 M⊙ , according to state-of-the-art models (Cushing et al. 2011).
During the past decade, ǫ Indi B was the closest brown
dwarf binary to the Sun, located at 3.626±0.009 pc from the
Sun (Scholz et al. 2003; McCaughrean et al. 2004). It has a
mean projected physical separation of 2.65 au (0.75 arcsec) and
⋆
Based on observations collected at the European Southern
Observatory, Chile, under DDT programme 290.C-5200(B) (PI Lodieu)
it is located at ∼1500 au from ǫ Indi A (Torres et al. 2006;
van Leeuwen 2007). It is the best studied pair of brown dwarfs
with the highest quality dataset to date (King et al. 2010). In
March 2013, Luhman (2013) announced the discovery of a
nearby brown dwarf with an optical spectral of L8 at a distance of 2.00±0.15 pc, WISE J104915.57−531906.1A, resolved
as a close binary (physical separation of 3 au) in the i-band.
Mamajek (2013) proposed to call this new nearby brown dwarf
binary Luhman 16AB due to its proximity to the Sun. The detection of the lithium in absorption at 6708Å in the optical spectrum of the primary Luhman (2013) and later in both components unambiguously places the system in the substellar regime
(Faherty et al. 2014). It is brighter than ǫ Indi B by 1.5 mag in J
and 2 mag in I. It is the third closest system to the Sun, after the
Centauri system and Barnard’s star. Thus, it represents the best
substellar system amenable for detailed characterisation of its
spectral energy distribution and a unique target to understand the
chemical processes at play at low temperatures and accross the
L/T transition (Burgasser et al. 2014). This system also provides
a rare opportunity to obtain high-resolution and high signal-tonoise spectroscopy at optical and infrared wavelengths to test the
mass-luminosity-age relation predicted by state-of-the-art mod-
1
The Link Between the Formation Rates of Clusters and Stars in
Galaxies
arXiv:1506.08846v1 [astro-ph.GA] 29 Jun 2015
Rupali Chandar,1 S. Michael Fall,2 and Bradley C. Whitmore2
ABSTRACT
The goal of this paper is to test whether the formation rate of star clusters
is proportional to the star formation rate (SFR) in galaxies. As a first step, we
present the mass functions of compact clusters younger than 10 Myr in seven
star-forming galaxies of diverse masses, sizes, and morphologies: the Large and
Small Magellanic Clouds, NGC 4214, NGC 4449, M83, M51, and the Antennae. These cluster mass functions (CMFs) are well represented by power laws,
dN/dM ∝ M β , with similar exponents β = −1.92 ± 0.27, but with amplitudes
that differ by factors up to ∼103 , corresponding to vast differences in the sizes of
the cluster populations in these galaxies. We then normalize these CMFs by the
SFRs in the galaxies, derived from dust-corrected Hα luminosities, and find that
the spread in the amplitudes collapses, with a remaining rms deviation of only
σ(log A) = 0.2. This is close to the expected dispersion from random uncertainties in the CMFs and SFRs. Thus, the data presented here are consistent with
exact proportionality between the formation rates of stars and clusters. However,
the data also permit weak deviations from proportionality, at the factor of two
level, within the statistical uncertainties. We find the same spread in amplitudes
when we normalize the mass functions of much older clusters, with ages in the
range 100 to 400 Myr, by the current SFR. This is another indication of the
general similarity among the cluster populations of different galaxies.
Subject headings: galaxies: individual (LMC, SMC, NGC 4214, NGC 4449, M83,
M51, Antennae) — galaxies: star clusters — stars: formation
1.
Introduction
Stars form together in clusters and associations, which in turn form in the densest
parts—the clumps—of molecular clouds (Lada & Lada 2003; McKee & Ostriker 2007). There
1
Department of Physics & Astronomy, The University of Toledo, Toledo, OH 43606
2
Space Telescope Science Institute, Baltimore, MD, USA
Mon. Not. R. Astron. Soc. 000, 1–?? (2013)
Printed 1 July 2015
(MN LATEX style file v2.2)
arXiv:1506.08844v1 [astro-ph.SR] 29 Jun 2015
Spectropolarimetry of SN 2011dh in M51: geometric
insights on a Type IIb supernova progenitor and explosion
Jon C. Mauerhan1⋆ , G. Grant Williams2,3, Douglas C. Leonard4, Paul S. Smith2,
Alexei V. Filippenko1, Nathan Smith2, Jennifer L. Hoffman5, Leah Huk5,
Kelsey I. Clubb1, Jeffrey M. Silverman6, S. Bradley Cenko7, Peter Milne2,
Avishay Gal-Yam8, Sagi Ben-Ami8
1 Department
of Astronomy, University of California, Berkeley, CA 94720-3411, USA
Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721, USA
3 MMT Observatory, Tucson, AZ 85721-0065, USA
4 Department of Astronomy, San Diego State University, PA-210, 5500 Campanile Drive, San Diego, CA 92182-1221
5 Department of Physics & Astronomy, University of Denver, 2112 East Wesley Avenue, Denver, CO 80208
6 Department of Astronomy, University of Texas at Austin, Austin, TX 78712, USA
7 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
8 Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel
2 Steward
1 July 2015
ABSTRACT
We present seven epochs of spectropolarimetry of the Type IIb supernova (SN) 2011dh
in M51, spanning 86 days of its evolution. The first epoch was obtained 9 days after
the explosion, when the photosphere was still in the depleted hydrogen layer of the
stripped-envelope progenitor. Continuum polarization is securely detected at the level
of P ≈ 0.5% through day 14 and appears to diminish by day 30, which is different from
the prevailing trends suggested by studies of other core-collapse SNe. Time-variable
modulations in P and position angle are detected across P-Cygni line features. Hα
and He i polarization peak after 30 days and exhibit position angles roughly aligned
with the earlier continuum, while O i and Ca ii appear to be geometrically distinct.
We discuss several possibilities to explain the evolution of the continuum and line
polarization, including the potential effects of a tidally deformed progenitor star, aspherical radioactive heating by fast-rising plumes of 56 Ni from the core, oblique shock
breakout, or scattering by circumstellar material. While these possibilities are plausible and guided by theoretical expectations, they are not unique solutions to the data.
The construction of more detailed hydrodynamic and radiative-transfer models that
incorporate complex aspherical geometries will be required to further elucidate the
nature of the polarized radiation from SN 2011dh and other Type IIb supernovae.
Key words: supernovae: general — supernovae: individual (SN 2011dh)
1
INTRODUCTION
Spectropolarimetric observations of supernovae (SNe) probe
the explosion geometry and the relative distribution of
chemical elements within the progenitor’s outer envelope
and inner ejecta (see review by Wang & Wheeler 2008). This
is valuable information that can provide clues to the nature
of the progenitor systems, the explosion mechanism, and the
kicks imparted to newborn neutron stars.
The most common source of linearly polarized emission
in SNe is Thomson scattering of photons by free electrons
⋆
E-mail: [email protected]
c 2013 RAS
in the dense ionized outflow or circumstellar medium. Optical scattering of photons by circumstellar dust particles
is another potentially important mechanism for efficiently
producing linear polarization (Wang & Wheeler 1996). However, in the idealized case of spherically symmetric geometry, every electric-field vector from the circular scattering
surface, as observed on the sky, will have an orthogonally
oriented vector of equal magnitude in an adjacent quadrant
of the circle, and will thus cancel out. The detection of net
polarization therefore requires some degree of asphericity
on the plane of the sky to break the symmetry. Net continuum polarization indicates the presence of global asphericity
for the electron-scattering photosphere and/or circumstellar
Mon. Not. R. Astron. Soc. 000, 000–000 (0000)
Printed July 1, 2015
(MN LaTEX style file v2.2)
Probing high-redshift galaxies with Lyα intensity mapping
arXiv:1506.08838v1 [astro-ph.CO] 29 Jun 2015
P.
Comaschi1? and A. Ferrara1,2
1
Scuola Normale Superiore, Piazza dei Cavalieri 7, 1-56126 Pisa, Italy
IPMU, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8583, Japan
2 Kavli
ABSTRACT
We present a study of the cosmological Lyα emission signal at z > 4. Our goal is to
predict the power spectrum of the spatial fluctuations that could be observed by an
intensity mapping survey. The model uses the latest data from the HST legacy fields
and the abundance matching technique to associate UV emission and dust properties with the halos, computing the emission from the interstellar medium (ISM) of
galaxies and the intergalactic medium (IGM), including the effects of reionization,
self-consistently. The Lyα intensity from the diffuse IGM emission is 1.3 (2.0) times
more intense than the ISM emission at z = 4(7); both components are fair tracers of
the star-forming galaxy distribution. However the power spectrum is dominated by
ISM emission on small scales (k > 0.01hMpc−1 ) with shot noise being significant only
above k = 1hMpc−1 . At very lange scales (k < 0.01hMpc−1 ) diffuse IGM emission
becomes important. The comoving Lyα luminosity density from IGM and galaxies,
40
−1
40
−1
Mpc−3
Mpc−3 and ρ˙ ISM
ρ˙ IGM
Lyα = 6.62(3.21) × 10 erg s
Lyα = 8.73(6.51) × 10 erg s
at z = 4(7), is consistent with recent SDSS determinations. We predict a power
k 3 P Lyα (k, z)/2π 2 = 9.76 × 10−4 (2.09 × 10−5 )nW2 m−4 sr−2 at z = 4(7) for k =
0.1hMpc−1 .
Key words: cosmology: observations - intergalactic and interstellar medium - intensity mapping - large-scale structure of universe
1
INTRODUCTION
According to the most popular cosmological framework, the
ΛCDM model, the astonishing diversity present in the local
universe originated from tiny density fluctuations in a homogeneous hot plasma. During the Hubble expansion, the
dark matter (DM) in the most overdense regions started to
collapse through gravitational instabilities, forming virialized halos where baryons could cool and form stars. This
process gave birth to primordial galaxies and, with billions
of years, every structure we can observe today. The impact
of these early objects on the subsequent cosmic evolution,
mediated by a number of feedback processes, has been dramatic; in addition, their radiative energy input powered the
last phase transition in the universe during the Epoch of
Reionization (EoR, (Barkana & Loeb 2001)).
It is quite surprising that, for fifty years, we have been
able to observe directly both the beginning, through the
CMB, and the ending of this process. However the study of
the ancient universe proved to be extremely challenging and
only in the last decade we have been able to explore the EoR
latest stages.
One of the main challenges is that the first galaxies are
?
Email: [email protected]
very faint and hard to detect even with our most powerful telescopes. Up to date, the deepest “drop-out” photometric surveys carried out by the Hubble Space Telescope
(HST), could detect ∼ 700 galaxies at z ≥ 8 (Bouwens et al.
2014a). Moreover, such sources are the most massive outliers
of the galaxy population and therefore bear little information about the sources producing the bulk of the ionizing
radiation (Salvaterra et al. 2011). This difficulty will likely
not be overcome by even the next generation of deep surveys, such as the JWST one.
For this reason, a different strategy must be designed,
which implies to forego the detection of individual sources
and probe directly their large scale distribution. This idea
can be implemented through the Intensity Mapping (IM) of
selected emission lines (Visbal & Loeb 2010; Visbal et al.
2011). Each point in space is identified by an angular coordinate and a redshift, that can be measured knowing the frequency of the emitted and detected photons. If the relevant
foregrounds can be removed, one can measure the distribution of the cumulative galaxy emission in coarse voxels. For
example, if the galaxy-galaxy correlation length is 1 Mpc
and we are interested in structures larger than 10 Mpc, we
can probe the sky in 10 Mpc voxels, corresponding to a spectral (angular) resolution λ/δλ ≈ 300 (θ ≈ 40 ) at z = 7, by
grouping together the signal of ∼ 1000 galaxies.
Mon. Not. R. Astron. Soc. 000, 1–14 (2015)
Printed 1 July 2015
(MN LATEX style file v2.2)
What are Protoclusters? – Defining High Redshift Galaxy
Clusters and Protoclusters
arXiv:1506.08835v1 [astro-ph.CO] 29 Jun 2015
Stuart I. Muldrew1⋆ , Nina A. Hatch2 and Elizabeth A. Cooke2
1 Department
2 School
of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK
Accepted 2015 June 27. Received 2015 June 16; in original form 2015 March 16.
ABSTRACT
We explore the structures of protoclusters and their relationship with high redshift
clusters using the Millennium Simulation combined with a semi-analytic model. We
find that protoclusters are very extended, with 90 per cent of their mass spread across
∼ 35 h−1Mpc comoving at z = 2 (∼ 30 arcmin). The ‘main halo’, which can manifest
as a high redshift cluster or group, is only a minor feature of the protocluster, containing less than 20 per cent of all protocluster galaxies at z = 2. Furthermore, many
protoclusters do not contain a main halo that is massive enough to be identified as
a high redshift cluster. Protoclusters exist in a range of evolutionary states at high
redshift, independent of the mass they will evolve to at z = 0. We show that the
evolutionary state of a protocluster can be approximated by the mass ratio of the
first and second most massive haloes within the protocluster, and the z = 0 mass of
a protocluster can be estimated to within 0.2 dex accuracy if both the mass of the
main halo and the evolutionary state is known. We also investigate the biases introduced by only observing star-forming protocluster members within small fields. The
star formation rate required for line-emitting galaxies to be detected is typically high,
which leads to the artificial loss of low mass galaxies from the protocluster sample.
This effect is stronger for observations of the centre of the protocluster, where the
quenched galaxy fraction is higher. This loss of low mass galaxies, relative to the field,
distorts the size of the galaxy overdensity, which in turn can contribute to errors in
predicting the z = 0 evolved mass.
Key words: methods: numerical – methods: statistical – galaxies: clusters: general
– galaxies: formation – galaxies: evolution – cosmology: theory
1
INTRODUCTION
In a cold dark matter universe with a cosmological constant
(ΛCDM), structure forms through hierarchical growth with
smaller haloes merging to form larger ones. Galaxy clusters
in the present day Universe are the most massive structures
to have formed and were the result of the merging of many
smaller haloes. Clusters, typically, are virialised dark matter
haloes of mass greater than 1014 M⊙ containing a hot X-ray
Intra-Cluster Medium (ICM) and red, passive galaxies.
At higher redshift, z > 1.5, most clusters were not
the massive virialised haloes that we see today. Instead we
see their progenitors, a diffuse collection of haloes that will
merge to make the final halo. The term ‘protocluster’ is often
used to describe this state, but differing definitions of what
a protocluster is exist in the literature. While some define
a protocluster as all the haloes at a given redshift that will
⋆
E-mail: [email protected]
c 2015 RAS
merge to make the final cluster, others define it as being just
the most massive progenitor halo, sometimes referred to as
the main halo. While using the latter definition dramatically
reduces the observational expense, it risks missing galaxies
undergoing environmental preprocessing and only captures
part of what is going on in the forming cluster.
Several high redshift galaxy clusters have now been
detected through X-ray emission, the Sunyaev-Zel’dovich
(SZ) effect, as well as through photometric redshift hunts in
large deep surveys (Gobat et al. 2011; Stanford et al. 2012;
Zeimann et al. 2012; Fassbender et al. 2014; Andreon et al.
2014). The properties of the ICM and galaxies indicate that
these structures are already collapsed, i.e. these objects are
single collapsed main haloes. However, a great deal of cluster
growth occurs at relatively late times (z < 1; Chiang et al.
2013), and many of the galaxies and dark matter that end
up in the z = 0 cluster, will not be located in the main
halo of the protocluster at high redshift. In this paper we
investigate how much of the matter and galaxies reside in
Mon. Not. R. Astron. Soc. 000, 1–11 (2011)
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(MN LATEX style file v2.2)
Cosmic voids in coupled dark energy cosmologies: the impact of
halo bias
arXiv:1506.08831v1 [astro-ph.CO] 29 Jun 2015
Giorgia Pollina1,4,5 , Marco Baldi1,2,3, Federico Marulli1,2,3, Lauro Moscardini1,2,3
1 Dipartimento
di Fisica e Astronomia, Alma Mater Studiorum Universit`a di Bologna, viale Berti Pichat, 6/2, I-40127 Bologna, Italy
- Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna, Italy
3 INFN - Sezione di Bologna, viale Berti Pichat 6/2, I-40127 Bologna, Italy
4 Universit¨
ats-Sternwarte M¨unchen, Fakult¨at f¨ur Physik, Ludwig-Maximilians Universit¨at M¨unchen, Scheinerstr. 1, D-81679 M¨unchen, Germany
5 Excellence Cluster Universe, Boltzmannstr. 2, D-85748 Garching, Germany
2 INAF
1 July 2015
ABSTRACT
In this work we analyse the properties of cosmic voids in standard and coupled dark energy
cosmologies. Using large numerical simulations, we investigate the effects produced by the
dark energy coupling on three statistics: the filling factor, the size distribution and the stacked
profiles of cosmic voids. We find that the bias of the tracers of the density field used to identify
the voids strongly influences the properties of the void catalogues, and, consequently, the possibility of using the identified voids as a probe to distinguish coupled dark energy models from
the standard ΛCDM cosmology. In fact, on one hand coupled dark energy models are characterised by an excess of large voids in the cold dark matter distribution as compared to the
reference standard cosmology, due to their higher normalisation of linear perturbations at low
redshifts. Specifically, these models present an excess of large voids with Reff > 20, 15, 12
h−1 Mpc , at z = 0, 0.55, 1, respectively. On the other hand, we do not find any significant
difference in the properties of the voids detected in the distribution of collapsed dark matter
halos. These results imply that the tracer bias has a significant impact on the possibility of
using cosmic void catalogues to probe cosmology.
Key words: dark energy – dark matter – cosmology: theory – galaxies: formation
1 INTRODUCTION
Despite the fact that the presently accepted standard cosmological model, the so-called ΛCDM scenario, appears to be
fully consistent with most of the available observations (see e.g.
Planck Collaboration et al. 2015a), it still presents some open issues in the detailed description of the distribution of matter at
small scales. One of such properties that still appears problematic is the observed abundance of dwarf galaxies in the underdense
regions of the Universe, which is found to be significantly lower
than what predicted by large N-body simulations carried out within
the ΛCDM cosmology. This problem, that was pointed out for the
first time by Peebles (2001), goes under the name of the void phenomenon, and it has been discussed by several authors over the past
years (see e.g. Tinker & Conroy 2009; Sutter et al. 2015a).
Besides the poor theoretical understanding of a cosmological constant as source of the observed accelerated expansion of the Universe (Weinberg 1989), the void phenomenon
is therefore one of the few observational tensions that motivate the investigation of alternative cosmological scenarios, together with the so-called cusp-core problem (de Blok 2010), the
satellite problem (Bullock 2010), the too big to fail problem
(Boylan-Kolchin, Bullock & Kaplinghat 2011), and the recently
c 2011 RAS
detected tension between the CMB- and cluster-based estimations
of σ8 , the r.m.s. of the mass density field within a sphere of radius
8 h−1 Mpc (Planck Collaboration et al. 2015b).
A relevant class of alternative cosmological models that has
been widely investigated in recent years is given by the so-called
coupled dark energy scenario (cDE hereafter, see e.g. Wetterich
1995; Amendola 2000, 2004; Farrar & Peebles 2004; Baldi 2011b).
In these models a dynamical scalar field sourcing the accelerated
cosmic expansion (see e.g. Wetterich 1988; Ratra & Peebles 1988)
is coupled to cold dark matter (CDM) particles resulting in a direct exchange of energy-momentum between these two cosmic
components. Such interaction gives rise to a new fifth force acting on CDM particles, possibly capable to make the voids emptier
(Nusser, Gubser & Peebles 2005). Other possible ways to address
the void phenomenon have been proposed, such as, for example,
a modification of gravity at very large scales (Li & Zhao 2009;
Clampitt, Cai & Li 2013; Spolyar, Sahl´en & Silk 2013).
The main effects of cDE models on the large-scale matter distribution in the Universe, as well as on the structural properties
of highly nonlinear collapsed objects (such as galaxies and galaxy
clusters), have been widely investigated in the recent past by several
works mostly based on dedicated large N-body simulations (see
Draft version July 1, 2015
Preprint typeset using LATEX style emulateapj v. 04/17/13
INTERRUPTED STELLAR ENCOUNTERS IN STAR CLUSTERS
Aaron M. Gellera,b
arXiv:1506.08830v1 [astro-ph.SR] 29 Jun 2015
Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy,
Northwestern University, 2145 Sheridan Rd, Evanston, IL 60208, USA and
Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Avenue, Chicago, IL 60637, USA
Nathan W. C. Leighc
Department of Astrophysics, American Museum of Natural History, Central Park West and 79th Street, New York, NY 10024 and
Department of Physics, University of Alberta, CCIS 4-183, Edmonton, AB T6G 2E1, Canada
Draft version July 1, 2015
ABSTRACT
Strong encounters between single stars and binaries play a pivotal role in the evolution of star
clusters. Such encounters can also dramatically modify the orbital parameters of binaries, exchange
partners in and out of binaries, and are a primary contributor to the rate of physical stellar collisions in
star clusters. Often, these encounters are studied under the approximation that they happen quickly
enough and within a small enough volume to be considered isolated from the rest of the cluster. In this
paper, we study the validity of this assumption through the analysis of a large grid of single – binary
and binary – binary scattering experiments. For each encounter we evaluate the encounter duration,
and compare this with the expected time until another single or binary star will join the encounter.
We find that for lower-mass clusters, similar to typical open clusters in our Galaxy, the percent of
encounters that will be “interrupted” by an interloping star or binary may be 20-40% (or higher) in the
core, though for typical globular clusters we expect .1% of encounters to be interrupted. Thus, the
assumption that strong encounters occur in relative isolation breaks down for certain clusters. Instead,
many strong encounters develop into more complex “mini-clusters”, which must be accounted for in
studying, for example, the internal dynamics of star clusters, and the physical stellar collision rate.
Subject headings: binaries: general — galaxies: star clusters: general — globular clusters: general
— open clusters and associations: general — stars: kinematics and dynamics —
methods: numerical
1. INTRODUCTION
The evolution of (collisional) star clusters is often conceptualized, at a basic level, as being governed by the
combination of the long-range cumulative effects of weak
stellar encounters, known as “two-body relaxation”, and
the results of short-range strong stellar encounters between individual stars and binaries. In Monte Carlo
models for globular cluster (GC) evolution, this assumption is more than a conceptual convenience, and is inherent to the functionality of the code (e.g. Spurzem
& Giersz 1996; Joshi et al. 2000; Vasiliev 2015). Twobody relaxation allows stars to gradually exchange energy, which evolves the cluster towards thermal equilibrium, and drives the processes of evaporation, mass segregation and core collapse. It has long been known that
close encounters with “hard” binaries (i.e., those with
relatively large binding energy compared to the kinetic
energies of cluster stars, Heggie 1975) can halt core collapse by donating energy to other stars in the encounter,
which can be given back to the cluster through two-body
relaxation processes. This type of strong encounter may
decrease the semi-major axis of the binary, and indeed,
strong encounters can modify all orbital parameters of binaries, exchange stars into and out of binaries, and even
result in physical stellar collisions. Moreover, strong ena [email protected]
b NSF Astronomy and
c [email protected]
Astrophysics Postdoctoral Fellow
counters are a key component to star cluster evolution
(Hut 1983), and they can alter a binary population from
its characteristics at birth (e.g. Ivanova et al. 2005; Hurley et al. 2007; Marks et al. 2011; Geller et al. 2013a,b,
2015; Leigh & Geller 2015).
As such, the outcomes of single – binary (1+2) and
binary – binary (2+2) encounters are well studied (e.g.
Heggie 1975; Hills 1975; Hut & Bahcall 1983; Fregeau
et al. 2004), and more recently stellar encounters involving triples are also gaining importance (Leigh & Geller
2012, 2013). Apart from direct N -body star cluster simulations (Aarseth 2003; Wang et al. 2015), it is typical
to make the simplifying assumption that such encounters
happen rapidly enough, and within a small enough volume, that they are effectively isolated from the rest of the
cluster. With such assumptions, one can run many fewbody scattering experiments, each involving perhaps 3-6
stars, to derive statistical cross sections of the outcomes
of such encounters (e.g. Hut & Bahcall 1983; Fregeau
et al. 2004), and apply this knowledge to help understand the more complex evolution of a full star cluster,
which itself may contain many hundreds to millions of
stars.
In this paper we investigate the validity of the assumption of treating these strong encounters as isolated. In reality the encounters occur within a star cluster, and most
often in the dense cluster core, where they may not be
allowed to progress fully on their own. More specifically,
we use the numerical scattering code FEWBODY (Fregeau
MNRAS 000, 1–24 (2015)
Preprint 1 July 2015
Compiled using MNRAS LATEX style file v3.0
The effects of metallicity, UV radiation and non-equilibrium
chemistry in high-resolution simulations of galaxies
A.
J. Richings1 and Joop Schaye1
1
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, the Netherlands
arXiv:1506.08829v1 [astro-ph.GA] 29 Jun 2015
1 July 2015
ABSTRACT
We present a series of hydrodynamic simulations of isolated galaxies with stellar
mass of 109 M . The models use a resolution of 750 M per particle and include a
treatment for the full non-equilibrium chemical evolution of ions and molecules (157
species in total), along with gas cooling rates computed self-consistently using the
non-equilibrium abundances. We compare these to simulations evolved using cooling
rates calculated assuming chemical (including ionisation) equilibrium, and we consider
a wide range of metallicities and UV radiation fields, including a local prescription for
self-shielding by gas and dust. We find higher star formation rates and stronger outflows at higher metallicity and for weaker radiation fields, as gas can more easily cool
to a cold (few hundred Kelvin) star forming phase under such conditions. Contrary
to variations in the metallicity and the radiation field, non-equilibrium chemistry generally has no strong effect on the total star formation rates or outflow properties.
However, it is important for modelling molecular outflows. For example, the mass
of H2 outflowing with velocities > 50 km s−1 is enhanced by a factor ∼ 20 in nonequilibrium. We also compute the observable line emission from Cii and CO. Both
are stronger at higher metallicity, while Cii and CO emission are higher for stronger
and weaker radiation fields respectively. We find that Cii is generally unaffected by
non-equilibrium chemistry. However, emission from CO varies by a factor of ∼ 2 − 4.
This has implications for the mean XCO conversion factor between CO emission and
H2 column density, which we find is lowered by up to a factor ∼ 2.3 in non-equilibrium,
and for the fraction of CO-dark molecular gas.
Key words: astrochemistry - ISM: atoms - ISM: molecules - galaxies: evolution galaxies: ISM.
1
INTRODUCTION
Hydrodynamic simulations of galaxy formation typically
model gas cooling by tabulating the cooling rate as a function of gas properties such as the density and temperature,
under certain assumptions. For example, the simplest approach, as used in some of the first cosmological hydrodynamic simulations (e.g. Katz et al. 1992), is to assume that
the gas has primordial abundances and is in collisional ionisation equilibrium (CIE). Sutherland & Dopita (1993) also
included the effects of metal-line cooling, computing cooling
curves in CIE for a range of metallicities.
Another effect that can be important for gas cooling is
the presence of a photoionising UV radiation field, which can
change the ionisation balance and heat the gas. Efstathiou
(1992) showed that an extragalactic UV background (UVB)
can suppress the cooling rate in a primordial plasma, thereby
inhibiting the formation of dwarf galaxies. Katz et al. (1996)
c 2015 The Authors
implemented primordial radiative cooling in the presence of
a UVB in cosmological hydrodynamic simulations.
Wiersma et al. (2009) considered the impact that a
photoionising UVB has on cooling rates in the presence of
metals. They showed that photoionisation can suppress the
cooling rate by up to an order of magnitude at temperatures and densities typical of the intergalactic medium (e.g.
104 K . T . 106 K, ρ/ hρi . 100). They also showed that
variations in relative abundances from their solar values can
change the cooling rate by a factor of a few. Wiersma et
al. (2009) tabulated the cooling rate from 11 elements separately in the presence of the redshift-dependent UVB of
Haardt & Madau (2001), and these tables have been used in
several cosmological hydrodynamic simulations (e.g. Crain
et al. 2009; Schaye et al. 2010, 2015; Hopkins et al. 2014).
The effects of metal cooling and UV radiation are particularly important below 104 K, as cooling from atomic hydrogen becomes inefficient at such temperatures. In primor-
Astrophysical Journal Letters, in press, 26 June 2015
Preprint typeset using LATEX style emulateapj v. 5/2/11
HIDING IN PLAIN SIGHT: RECORD-BREAKING COMPACT STELLAR SYSTEMS
IN THE SLOAN DIGITAL SKY SURVEY
Michael A. Sandoval1 , Richard P. Vo1,2 , Aaron J. Romanowsky1,3 , Jay Strader4 , Jieun Choi5,6 ,
Zachary G. Jennings6 , Charlie Conroy5 , Jean P. Brodie3 , Caroline Foster7 , Alexa Villaume6 ,
Mark A. Norris8 , Joachim Janz9 , Duncan A. Forbes9
arXiv:1506.08828v1 [astro-ph.GA] 29 Jun 2015
Astrophysical Journal Letters, in press, 26 June 2015
ABSTRACT
Motivated by the recent, serendipitous discovery of the densest known galaxy, M60-UCD1,
we present two initial findings from a follow-up search, using the Sloan Digital Sky Survey,
Subaru/Suprime-Cam and Hubble Space Telescope imaging, and SOAR/Goodman spectroscopy. The
first object discovered, M59-UCD3, has a similar size to M60-UCD1 (half-light radius of rh ∼ 20 pc)
but is 40% more luminous (MV ∼ −14.6), making it the new densest-known galaxy. The second, M85HCC1, has a size like a typical globular cluster (rh ∼ 1.8 pc) but is much more luminous (MV ∼ −12.5).
This hypercompact cluster is by far the densest confirmed free-floating stellar system, and is equivalent to the densest known nuclear star clusters. From spectroscopy, we find that both objects are
relatively young (∼ 9 Gyr and ∼ 3 Gyr, respectively), with metal-abundances that resemble those of
galaxy centers. Their host galaxies show clear signs of large-scale disturbances, and we conclude that
these dense objects are the remnant nuclei of recently accreted galaxies. M59-UCD3 is an ideal target
for follow-up with high-resolution imaging and spectroscopy to search for an overweight central supermassive black hole as was discovered in M60-UCD1. These findings also emphasize the potential
value of ultra-compact dwarfs and massive globular clusters as tracers of the assembly histories of
galaxies.
Subject headings: galaxies: fundamental parameters — galaxies: nuclei — galaxies: star clusters:
general
1. INTRODUCTION
The classic distinction between galaxies and star clusters was riven by the discovery of stellar systems with
intermediate sizes and luminosities: the ultracompact
dwarfs (UCDs; Hilker et al. 1999; Drinkwater et al. 2000).
The nature and origins of these novel objects have been
debated ever since, with potentially important implications for how star clusters and galaxies form and evolve—
tracing novel modes of star formation, cluster merging,
and/or episodes of satellite galaxy accretion (e.g., Fellhauer & Kroupa 2002; Pfeffer et al. 2014).
The UCDs were previously overlooked, not because
they were extremely rare, nor especially difficult to observe, but because they did not fit in with preconceptions about known object types. They were, therefore,
filtered out during the focused search process (cf. similar oversights discussed in Simons & Chabris 1999; Drew
1 Department of Physics and Astronomy, San Jos´
e State University, One Washington Square, San Jose, CA 95192, USA
2 Department of Physics and Astronomy, San Francisco State
University, San Francisco, CA, 94131, USA
3 University of California Observatories, 1156 High Street,
Santa Cruz, CA 95064, USA
4 Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA
5 Harvard–Smithsonian Center for Astrophysics, 60 Garden
Street, Cambridge, MA 02138, USA
6 Department of Astronomy and Astrophysics, University of
California, Santa Cruz, CA 95064, USA
7 Australian Astronomical Observatory, PO Box 915, North
Ryde, NSW 1670, Australia
8 Max Planck Institut f¨
ur Astronomie, K¨
onigstuhl 17, D69117, Heidelberg, Germany
9 Centre for Astrophysics & Supercomputing, Swinburne University, Hawthorn, VIC 3122, Australia
et al. 2013). To those using ground-based imaging to
study extragalactic globular clusters (GCs), the UCDs
were deemed too bright, and assumed to be foreground
stars. To those using the Hubble Space Telescope (HST),
whose fine spatial resolution is well suited for appreciating the extended nature of the UCDs, they appeared too
diffuse, and were seen as background galaxies.
Despite this lesson in selection bias, years of research
on UCDs ensued without questioning whether or not the
parameter space of their properties had been adequately
mapped out. The impact of this shortcoming was exemplified by the emphasis on an apparent size–luminosity
relation for UCDs (e.g., Kissler-Patig et al. 2006; Murray
2009; Gieles et al. 2010), which was later argued to be
merely a consequence of observational limitations at low
surface-brightnesses, with the population of large UCDs
actually extending to much lower luminosities (Brodie et
al. 2011).
It was also assumed that UCDs were restricted to highdensity environments, as they were first identified around
the central galaxies in the Fornax and Virgo clusters, and
indeed had earlier been predicted to form in this context
(Bassino et al. 1994). However, UCDs were subsequently
found around ordinary field galaxies, implying that their
formation does not require such particular circumstances
(Hau et al. 2009; Norris & Kannappan 2011; Norris et al.
2014, N+14 hereafter).
As a recent step toward a broader understanding of
UCDs and other compact stellar systems, Strader et
al. (2012) analyzed a mosaic of HST/Advanced Camera for Surveys (ACS) images of the Virgo giant elliptical galaxy M60 (NGC 4649), and scrutinized all the
detected objects to consider whether they might be as-
MNRAS 000, 1–?? (2015)
Preprint 1 July 2015
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Neutrino-driven explosions of ultra-stripped type Ic
supernovae generating binary neutron stars
arXiv:1506.08827v1 [astro-ph.HE] 29 Jun 2015
Yudai Suwa1,2⋆ , Takashi Yoshida1, Masaru Shibata1, Hideyuki Umeda3,
and
Koh Takahashi3
1
Yukawa Institute for Theoretical Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto, 606-8502, Japan
f¨
ur Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching, Germany
3 Department of Astronomy, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan
2 Max-Planck-Institut
Accepted. Received.
ABSTRACT
We study explosion characteristics of ultra-stripped supernovae (SNe), which are candidates of SNe generating binary neutron stars (NSs). As a first step, we perform stellar
evolutionary simulations of bare carbon-oxygen cores of mass from 1.45 to 2.0 M⊙ until the iron cores become unstable and start collapsing. We then perform axisymmetric
hydrodynamics simulations with spectral neutrino transport using these stellar evolution outcomes as initial conditions. All models exhibit successful explosions driven
by neutrino heating. The diagnostic explosion energy, ejecta mass, Ni mass, and NS
mass are typically ∼ 1050 erg, ∼ 0.1M⊙, ∼ 0.01M⊙, and ≈ 1.3M⊙, which are compatible with observations of rapidly-evolving and luminous transient such as SN 2005ek.
We also find that the ultra-stripped SN is a candidate for producing the secondary
low-mass NS in the observed compact binary NSs like PSR J0737-3039.
Key words: binaries: close — stars: evolution — stars: massive — stars: neutron —
supernovae: general — supernovae: individual (SN 2005ek)
1
INTRODUCTION
Mergers of binary compact objects, i.e. neutron stars
(NSs) and black holes (BHs), are promising candidates of
strong gravitational wave (GW) sources. Event rates of
these mergers are estimated based on the number of observed binary NSs in our galaxy and population synthesis calculations (e.g., Abadie et al. 2010). These estimates,
however, have large uncertainty with, roughly speaking,
two orders of magnitude. Recalling that the compact objects are formed through gravitational collapse and subsequent supernova (SN) explosions, there should be transient events generating binary compact objects observable by electromagnetic waves. SN surveys by currently
working facilities e.g., The Subaru Hyper Suprime-Cam
(HSC; Miyazaki et al. 2012; Tominaga et al. 2014), Palomar Transient Factory (PTF; Rau et al. 2009; Law et al.
2009), Catalina Real-Time Sky Survey (CRTS; Drake et al.
2009), Panoramic Survey Telescope & Rapid Response System (Pan-STARRS1; Kaiser et al. 2010), and SkyMapper
(Keller et al. 2007), and also by coming future projects (e.g.,
Large Synoptic Survey Telescope1 ; LSST) will be able to
⋆
1
E-mail: [email protected]
http://www.lsst.org/lsst/
c 2015 The Authors
give constraints on the formation rate of transient objects
including binary compact objects.
One of the possible candidates for a SN forming a close
binary system is ultra-stripped SN (Tauris et al. 2015), which
is peculiar type Ic SN with a faint and fast decaying light
curve. Peak luminosity of Type Ic SNe is mainly determined
by the ejected mass of 56 Ni, M56 Ni , while the timescale
around the peak is determined by the diffusion timescale
3/4 −1/4
τc ∝ Mej EK , where Mej is the ejecta mass and EK is
the kinetic energy of the ejecta (Arnett 1982). Therefore,
the low peak luminosity and short characteristic time imply
the small masses of the ejecta and 56 Ni. For instance, SN
2005ek is one of these SNe (Drout et al. 2013; Tauris et al.
2013), whose estimated ejecta mass, ∼ O(0.1)M⊙ is notably
smaller than typical SN Ic, O(1)M⊙ (Drout et al. 2011), as
well as smaller 56 Ni mass, and the explosion energy is also
smaller by an order of magnitude (O(1050 ) erg) than typical core-collapse SNe (O(1051 ) erg). To model these rapidlyevolving SNe with small ejecta mass, the progenitor stars are
thought to be stripped much more than canonical strippedenvelope type Ib/c SNe, that is, ultra-stripped SNe coined by
Tauris et al. (2013); Tauris et al. (2015). Besides SN 2005ek
and other known SNe, ten rapidly-evolving transients were
recently detected by Pan-STARRS1, which exhibit shorter
decaying timescale (∼ 10 days) than canonical SNe with
Draft version July 1, 2015
Preprint typeset using LATEX style emulateapj v. 5/2/11
VISCOUS BOUNDARY LAYERS OF RADIATION-DOMINATED, RELATIVISTIC JETS. I. THE
TWO-STREAM MODEL
Eric R. Coughlin1 and Mitchell C. Begelman1
arXiv:1506.08824v1 [astro-ph.HE] 29 Jun 2015
JILA, University of Colorado and National Institute of Standards and Technology, 440 UCB, Boulder, CO 80309
Draft version July 1, 2015
ABSTRACT
Using the relativistic equations of radiation hydrodynamics in the viscous limit, we analyze the
boundary layers that develop between radiation-dominated jets and their environments. In this paper
we present the solution for the self-similar, 2-D, plane-parallel two-stream problem, wherein the jet
and the ambient medium are considered to be separate, interacting fluids, and we compare our results
to those of previous authors. (In a companion paper we investigate an alternative scenario, known as
the free-streaming jet model.) Consistent with past findings, we show that the boundary layer that
develops between the jet and its surroundings creates a region of low-density material. These models
may be applicable to sources such as super-Eddington tidal disruption events and long gamma-ray
bursts.
Subject headings: galaxies: jets — gamma-ray bursts: general — radiation: dynamics — relativistic
processes
1. INTRODUCTION
Astrophysical jets almost certainly exist as aggregates
of massive particles, magnetic fields, and radiation. In
certain scenarios, however, the contribution of radiation
to the energetics of the outflow far outweighs those of
the particles and magnetic fields, meaning that one can
essentially neglect the presence of the latter two entities.
One such scenario occurs in the collapsar model
of long gamma-ray bursts (GRBs; Woosley 1993;
MacFadyen & Woosley 1999). In this model, the core of
a massive, evolved star collapses directly (or with a shortlived neutron star phase) to a black hole during the infall
stage of a type-II supernova. The energy released by the
material accreting onto the black hole, and ultimately
observed as the gamma-ray emission, is collimated into
bipolar jets – the jet formation confirmed by energetics arguments (Waxman et al. 1998; Fruchter et al. 1999;
Frail et al. 2001) and the observations of breaks in the Xray afterglow light curves (Panaitescu 2007; Dado et al.
2008; Racusin et al. 2009) – and is often sufficient to
unbind the stellar envelope, resulting in a supernova
(Galama et al. 1998; Bersier et al. 2004; Kamble et al.
2009; Levan et al. 2014, but see Fynbo et al. 2006). If
one assumes that the mass of the remnant black hole
is on the order of a few solar masses, its accretion luminosity exceeds the Eddington limit by roughly ten
orders of magnitude, meaning that radiation pressure,
even if the flux is nearly isotropic, is likely an important mechanism for driving and sustaining the outflow
(the fireball model; Rees & Mészáros 1992). Even if
the jet is launched by magnetohydrodynamical mechanisms (Blandford & Znajek 1977; Blandford & Payne
1982), radiation could still play a prominent role in determining the dynamics of the jet. Arguments concerning
the time necessary for the jet to break through the stellar
envelope also seem to disfavor Poynting-dominated jets
[email protected], [email protected]
1 Department of Astrophysical and Planetary Sciences, University of Colorado, UCB 391, Boulder, CO 80309
(Bromberg et al. 2015; but see Mundell et al. 2013).
Jets produced during tidal disruption events (TDEs;
Giannios & Metzger 2011) – when a star is destroyed by
the tidal force of a supermassive black hole – could provide another class of radiation-dominated outflow. After
the star is tidally disrupted, roughly half of the shredded debris remains bound to the black hole and returns
to the tidal disruption radius. If the black hole has
a mass less than roughly 107 M⊙ , that rate of return
can exceed the Eddington limit of the black hole by orders of magnitude for a significant amount of time (on
the order of days to months; Evans & Kochanek 1989;
Strubbe & Quataert 2009). Provided that this material
can rapidly accrete onto the black hole, which is likely
the case due to the tidal dissipation of kinetic energy
(Kochanek 1994; Guillochon et al. 2014) and relativistic
precession effects (Rees 1988; Evans & Kochanek 1989),
the energy released during the accretion process will also
be supercritical. It was during this supercritical phase
that the event Swift J1644+57 was seen to have an associated jetted outflow (Burrows et al. 2011; Bloom et al.
2011; Cannizzo et al. 2011; Zauderer et al. 2011) (the
source Swift J2058+05 may provide another example of
a jetted, super-Eddington TDE; Cenko et al. 2012). Although the jet launching mechanism for this event is uncertain, the magnetic field of the tidally-disrupted star,
assuming its flux is approximately conserved, is almost
certainly insufficient to power the outflow. Therefore,
unless one invokes the existence of a fossil magnetic field
(Tchekhovskoy et al. 2014; Kelly et al. 2014), the radiation pressure associated with the accretion luminosity
likely plays some role in powering the jet. At any rate,
the radiation released during the supercritical accretion
process affects the dynamics of the collimated outflow
and contributes substantially to its overall energy and
momentum.
Collapsar jets inject a significant amount of energy
into the overlying stellar envelope as they punch their
way into the circumstellar medium, creating a pressurized “cocoon” of shocked material with which the
Mon. Not. R. Astron. Soc. 000, 000–000 (0000)
Printed 1 July 2015
(MN LATEX style file v2.2)
arXiv:1506.08822v1 [astro-ph.GA] 29 Jun 2015
Neutral hydrogen gas, past and future star-formation in galaxies in
and around the ‘Sausage’ merging galaxy cluster
Andra Stroe1? , Tom Oosterloo2,3 , Huub J. A. R¨ottgering1 , David Sobral1,4,5 †,
Reinout
van Weeren6 ‡, William Dawson7
1
Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands
Postbus 2, NL-7990 AA Dwingeloo, The Netherlands
3 Kapteyn Astronomical Institute, Postbus 800, NL-9700 AV Groningen, The Netherlands
4 Instituto de Astro´ısica e Ciˆ
encias do Espac¸o, Universidade de Lisboa, Observat´orio Astron´omico de Lisboa, Tapada da Ajuda, 1359-018, Lisbon, Portugal
5 Departamento de F´ısica, Faculdade de Ciˆ
encias, Universidade de Lisboa, Edif´ıcio C8, Campo Grande, 1748-016, Lisbon, Portugal
6 Harvard Smithsonian Center for Astrophysics (CfA - SAO), 60 Garden Street Cambridge, MA 02138, US
4 Lawrence Livermore National Laboratory, P.O. Box 808 L-210, Livermore, CA, 94551, USA
2 ASTRON,
1 July 2015
ABSTRACT
CIZA J2242.8+5301 (z = 0.188, nicknamed ‘Sausage’) is an extremely massive (M200 ∼
2.0 × 1015 M ), merging cluster with shock waves towards its outskirts, which was found
to host numerous emission-line galaxies. We performed extremely deep Westerbork Synthesis Radio Telescope HI observations of the ‘Sausage’ cluster to investigate the effect of the
merger and the shocks on the gas reservoirs fuelling present and future star formation (SF)
in cluster members. By using spectral stacking, we find that the emission-line galaxies in the
‘Sausage’ cluster have, on average, as much HI gas as field galaxies (when accounting for the
fact cluster galaxies are more massive than the field galaxies), contrary to previous studies.
Since the cluster galaxies are more massive than the field spirals, they may have been able to
retain their gas during the cluster merger. The large HI reservoirs are expected to be consumed
within ∼ 0.75 − 1.0 Gyr by the vigorous SF and AGN activity and/or driven out by the outflows we observe. We find that the star-formation rate in a large fraction of Hα emission-line
cluster galaxies correlates well with the radio broad band emission, tracing supernova remnant
emission. This suggests that the cluster galaxies, all located in post-shock regions, may have
been undergoing sustained SFR for at least 100 Myr. This fully supports the interpretation
proposed by Stroe et al. (2015) and Sobral et al. (2015) that gas-rich cluster galaxies have
been triggered to form stars by the passage of the shock.
Key words: galaxies: active, galaxies: clusters: individual: CIZA J2242.8+5301, shock
waves, radio continuum: galaxies, radio lines: galaxies
1
INTRODUCTION
Galaxy cluster environments have a profound impact on the evolution of cluster galaxies. At low redshifts (z < 0.5) and focusing
on relaxed clusters, the fraction of galaxies which are star-forming
drops steeply from field environments, to cluster outskirts and cores
(Dressler 1980; Balogh et al. 1998; Goto et al. 2003). The morphological transformation of field spirals into cluster ellipticals or S0s
has been attributed to a number of processes. The dense intracluster
medium (ICM) could lead to the ram pressure stripping of the gas
content of field spirals as they accrete onto the cluster (e.g. Gunn
& Gott 1972; Fumagalli et al. 2014). Tidal forces produced by gradients in the cluster gravitational potential or by encounters with
?
E-mail: [email protected]
† VENI/IF Fellow
‡ Einstein Fellow
other galaxies, can distort infalling galaxies, truncate their halo and
disk (harassment, Moore et al. 1996) or remove gas contained in
the galaxy and deposit it into the ICM (strangulation, Larson et al.
1980). All these processes ultimately lead to the removal of gas and
a truncation of star-formation (SF).
The effect of relaxed cluster environments on galaxies is evident using a wide range of diagnostics, which trace different phases
and time-scales of SF. Using UV data produced by young OB stars,
Owers et al. (2012) found galaxies with star-forming trails, which
they attribute to gas compression by the high-pressure merger environment. The UV radiation coming from massive, short-lived stars
˚ probe SF
excites emission lines. Lines such as Hα or [OII]3727A
on time scales of < 10 Myr. Emission line studies confirm that the
fraction of star-forming galaxies increases from cluster cores towards field environments (e.g. Gavazzi et al. 1998; Balogh et al.
1998; Finn et al. 2005; Sobral et al. 2011; Darvish et al. 2014).
Using far infra-red data (tracing dust obscured SF), Rawle et al.
Mon. Not. R. Astron. Soc. 000, 1–10 (2015)
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(MN LATEX style file v2.2)
arXiv:1506.08821v1 [astro-ph.GA] 29 Jun 2015
Evolution of mid-infrared galaxy luminosity functions from the
entire AKARI NEP-Deep field with new CFHT photometry
Tomotsugu Goto1⋆, Nagisa Oi2 , Youichi Ohyama3 , Matthew Malkan4 ,
Hideo Matsuhara2, Takehiko Wada2, Marios Karouzos5,
Myungshin Im5 , Takao Nakagawa2 , Veronique Buat6 , Denis Burgarella6,
Chris Sedgwick7 , Yoshiki Toba8 , Woong-Seob Jeong9,10,
Lucia Marchetti7 , Katarzyna Małek11,12,Ekaterina Koptelova1 ,
Dani Chao1, Yi-Han Wu1, Chris Pearson7,13,14, Toshinobu Takagi2 ,
Hyung Mok Lee5 , Stephen Serjeant7 , Tsutomu T. Takeuchi11, and Seong Jin Kim5,10
1 National
Tsing hua University, No. 101, Section 2, Kuang-Fu Road, Hsinchu, Taiwan 30013
of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa 252-5210
3 Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 106, Taiwan
4 Department of Physics and Astronomy, UCLA, Los Angeles, CA, 90095-1547, USA
5 Astronomy Program, Department of Physics & Astronomy, FPRD, Seoul National University, Shillim-Dong, Kwanak-Gu, Seoul 151-742, Korea
6 Aix-Marseille Universit, CNRS LAM (Laboratoire dAstrophysique de Marseille) UMR 7326, 13388 Marseille, France
7 Department of Physics, The Open University, Milton Keynes, MK7 6AA, UK
8 Research Center for Space and Cosmic Evolution, Ehime University, Bunkyo-cho, Matsuyama 790-8577, Japan
9 Korea Astronomy and Space Science Institute 61-1, Hwaam-dong, Yuseong-gu, Daejeon, Republic of Korea 305-348
10 Korea University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 305-350, Republic of Korea
11 Institute for Advanced Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601
12 National Centre for Nuclear Research, ul. Hoza 69, 00-681 Warszawa, Poland
13 RAL Space, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK
14 Oxford Astrophysics, Denys Wilkinson Building, University of Oxford, Keble Rd, Oxford OX1 3RH, UK
2 Institute
1 July 2015; in original form 2015 February 20
ABSTRACT
We present infrared galaxy luminosity functions (LFs) in the AKARI North Ecliptic Pole
(NEP) deep field using recently-obtained, wider CFHT optical/near-IR images. AKARI
has obtained deep images in the mid-infrared (IR), covering 0.6 deg2 of the NEP deep
field. However, our previous work was limited to the central area of 0.25 deg2 due to
the lack of optical coverage of the full AKARI NEP survey. To rectify the situation,
we recently obtained CFHT optical and near-IR images over the entire AKARI NEP
deep field. These new CFHT images are used to derive accurate photometric redshifts,
allowing us to fully exploit the whole AKARI NEP deep field.
AKARI’s deep, continuous filter coverage in the mid-IR wavelengths (2.4, 3.2, 4.1,
7, 9, 11, 15, 18, and 24µm) exists nowhere else, due to filter gaps of other space telescopes. It allows us to estimate restframe 8µm and 12µm luminosities without using a
large extrapolation based on spectral energy distribution (SED) fitting, which was the
largest uncertainty in previous studies. Total infrared luminosity (TIR) is also obtained
more reliably due to the superior filter coverage. The resulting restframe 8µm, 12µm,
and TIR LFs at 0.15 < z < 2.2 are consistent with previous works, but with reduced
uncertainties, especially at the high luminosity-end, thanks to the wide field coverage.
In terms of cosmic infrared luminosity density (ΩIR ), we found that the ΩIR evolves as
∝ (1 + z)4.2±0.4 .
1 INTRODUCTION
Studies of the extragalactic background suggest that at least half
the luminous energy generated by stars has been reprocessed
into the infrared (IR) emission by dust grains (Lagache et al.
1999; Puget et al. 1996; Franceschini et al. 2008), indicating
that dust-obscured star formation (SF) was more important at
higher redshifts than today.
c 2015 RAS
Takeuchi et al. (2005a) reported that the IR-to-UV luminosity density ratio, ρL(dust) /ρL(U V ) evolves from 3.75 (z=0)
to 15.1 by z=1.0, after a careful treatment of the sample selection
effects. Goto et al. (2010b) suggested that total infrared (TIR)
luminosity accounts for ∼70% of total star formation rate (SFR)
density at z=0.25, and 90% by z=1.3. These results highlight
the importance of probing cosmic star formation activity at high
redshift in the infrared bands.
arXiv:1506.08820v1 [astro-ph.GA] 29 Jun 2015
**Volume Title**
ASP Conference Series, Vol. **Volume Number**
**Author**
c **Copyright Year** Astronomical Society of the Pacific
Cosmic star formation history and AGN evolution near and far:
from AKARI to SPICA
Tomotsugu Goto1 , Takehiko Wada2 , Hideo Matsuhara2 , AKARI NEP team,
AKARI all sky survey team, and SPICA MCS team
1 Dark
Cosmology Centre, Niels Bohr Institute, Denmark
2 Institute
of Space and Astronautical Science, JAXA, Japan
Abstract. Infrared (IR) luminosity is fundamental to understanding the cosmic star
formation history and AGN evolution, since their most intense stages are often obscured
by dust. Japanese infrared satellite, AKARI, provided unique data sets to probe these
both at low and high redshifts. The AKARI performed an all sky survey in 6 IR bands
(9, 18, 65, 90, 140, and 160µm) with 3-10 times better sensitivity than IRAS, covering
the crucial far-IR wavelengths across the peak of the dust emission. Combined with
a better spatial resolution, AKARI can measure the total infrared luminosity (LT IR ) of
individual galaxies much more precisely, and thus, the total infrared luminosity density
of the local Universe. In the AKARI NEP deep field, we construct restframe 8µm,
12µm, and total infrared (TIR) luminosity functions (LFs) at 0.15< z <2.2 using 4128
infrared sources. A continuous filter coverage in the mid-IR wavelength (2.4, 3.2, 4.1,
7, 9, 11, 15, 18, and 24µm) by the AKARI satellite allows us to estimate restframe 8µm
and 12µm luminosities without using a large extrapolation based on a SED fit, which
was the largest uncertainty in previous work. By combining these two results, we reveal
dust-hidden cosmic star formation history and AGN evolution from z=0 to z=2.2, all
probed by the AKARI satellite. The next generation space infrared telescope, SPICA,
will revolutionize our view of the infrared Universe with superb sensitivity of the cooled
3m space telescope. We conclude with our survey proposal and future prospects with
SPICA.
1.
1.1.
Lessons from AKARI
Background
Revealing the cosmic star formation history is one of the major goals of observational
astronomy. However, UV/optical estimation only provides us with a lower limit of
the star formation rate (SFR) due to obscuration by dust. A straightforward way to
overcome this problem is to observe in the infrared, which can capture star formation
activity invisible in the UV. The superb sensitivities of Spitzer and AKARI satellites
have revolutionized the field.
In the local Universe, often used IR LFs are from the IRAS (e.g., Sanders et al.
2003; Goto et al. 2011b) from 1980s, with only several hundred galaxies. In addition,
bolometric infrared luminosities (LIR,8−1000µm ) of local galaxies were estimated using
equation in P´erault (1987), which was a simple polynomial, obtained assuming a simple
blackbody and dust emissivity. Furthermore, the reddest filter of IRAS was 100µm,
which did not span the peak of the dust emission for most galaxies, leaving a great deal
1
arXiv:1506.08818v1 [astro-ph.EP] 29 Jun 2015
On the existence of regular and irregular outer moons orbiting
the Pluto-Charon system
Erez Michaely, Hagai B. Perets and Evgeni Grishin
Physics Department, Technion - Israel Institute of Technology, Haifa 3200004, Israel
Received
;
accepted
–2–
Abstract
The dwarf planet Pluto is known to host an extended system of five co-planar
satellites. Previous studies have explored the formation and evolution of the system in isolation, neglecting perturbative effects by the Sun. Here we show that
secular evolution due to the Sun can strongly affect the evolution of outer satellites and rings in the system, if such exist. Although precession due to extended
gravitational potential from the inner Pluto-Charon binary quench such secular
evolution up to acrit ∼ 0.0035 AU (∼ 0.09 RHill the Hill radius; including all of
the currently known satellites), outer orbits can be significantly altered. In particular, we find that co-planar rings and satellites should not exist beyond acrit ;
rather, satellites and dust particles in these regions secularly evolve on timescales
ranging between 104 − 106 yrs, and quasi-periodically change their inclinations
and eccentricities through secular evolution (Lidov-Kozai oscillations). Such oscillations can lead to high inclinations and eccentricities, constraining the range
where such satellites (and dust particles) can exist without crossing the orbits
of the inner satellites, or crossing the outer Hill stability range. Outer satellites,
if such exist are therefore likely to be irregular satellites, with orbits limited to
be non-circular and/or highly inclined. These could be potentially detected and
probed by the New-Horizon mission, possibly providing direct evidence for the
secular evolution of the Pluto satellite system, and shedding new light on its
origins.
Limits on anisotropy in the nanohertz stochastic gravitational-wave background
S. R. Taylor,1, 2, ∗ C. M. F. Mingarelli,3, 4, 5 J. R. Gair,2 A. Sesana,5, 6 G. Theureau,7, 8, 9 S. Babak,6 C. G. Bassa,10, 11 P.
Brem,6 M. Burgay,12 R. N. Caballero,4 D. J. Champion,4 I. Cognard,7, 8 G. Desvignes,4 L. Guillemot,7, 8 J. W.
T. Hessels,10, 13 G. H. Janssen,10, 11 R. Karuppusamy,4 M. Kramer,4, 11 A. Lassus,4, 7 P. Lazarus,4 L. Lentati,14
K. Liu,4 S. Osłowski,15, 4 D. Perrodin,12 A. Petiteau,16 A. Possenti,12 M. B. Purver,11 P. A. Rosado,17, 18
S. A. Sanidas,11, 13 R. Smits,10 B. Stappers,11 C. Tiburzi,12, 19 R. van Haasteren,1 A. Vecchio,5 and J. P. W. Verbiest15, 4
arXiv:1506.08817v1 [astro-ph.HE] 29 Jun 2015
1
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA
2
Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
3
TAPIR (Theoretical Astrophysics), California Institute of Technology MC 350-17, Pasadena, California 91125, USA
4
Max-Planck-Institut f¨ur Radioastronomie, Auf dem H¨ugel 69, D-53121 Bonn, Germany
5
School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom
6
Max-Planck-Institut f¨ur Gravitationsphysik, Albert Einstein Institut, Am M¨uhlenberg 1, 14476 Golm, Germany
7
Laboratoire de Physique et Chimie de l’Environnement et de l’Espace LPC2E CNRS-Universit´e d’Orl´eans, F-45071 Orl´eans, France
8
Station de radioastronomie de Nanc¸ay, Observatoire de Paris, CNRS/INSU F-18330 Nanc¸ay, France
9
Laboratoire Univers et Th´eories LUTh, Observatoire de Paris, CNRS/INSU,
Universit´e Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
10
ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA, Dwingeloo, The Netherlands
11
Jodrell Bank Centre for Astrophysics, University of Manchester, Manchester, M13 9PL, United Kingdom
12
INAF - Osservatorio Astronomico di Cagliari, via della Scienza 5, I-09047 Selargius (CA), Italy
13
Anton Pannekoek Institute for Astronomy, University of Amsterdam,
Science Park 904, 1098 XH Amsterdam, The Netherlands
14
Astrophysics Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge, CB3 0HE, UK
15
Fakult¨at f¨ur Physik, Universit¨at Bielefeld, Postfach 100131, 33501 Bielefeld, Germany
16
Universit´e Paris-Diderot-Paris7 APC - UFR de Physique, Batiment Condorcet,
10 rue Alice Domont et L´eonie Duquet 75205 PARIS CEDEX 13, France
17
Centre for Astrophysics & Supercomputing, Swinburne University of Technology, PO Box 218, Hawthorn VIC 3122, Australia
18
Max Planck Institute for Gravitational Physics, Albert Einstein Institute, Callinstraße 38, 30167, Hanover, Germany
19
Dipartimento di Fisica - Universit´a di Cagliari, Cittadella Universitaria, I-09042 Monserrato (CA), Italy
(Dated: July 1, 2015)
The paucity of observed supermassive black hole binaries (SMBHBs) may imply that the gravitational
wave background (GWB) from this population is anisotropic, rendering existing analyses sub-optimal.
We present the first constraints on the angular distribution of a nanohertz stochastic GWB from circular,
inspiral-driven SMBHBs using the 2015 European Pulsar Timing Array data [1]. Our analysis of the GWB
in the ∼ 2 − 90 nHz band shows consistency with isotropy, with the strain amplitude in l > 0 spherical
harmonic multipoles . 40% of the monopole value. We expect that these more general techniques will
become standard tools to probe the angular distribution of source populations.
PACS numbers: 04.80.Nn, 04.25.dg, 95.85.Sz, 97.80.-d 97.60.Gb 04.30.-w
Introduction.– Pulsar Timing Arrays (PTAs) are currently being used to search for, and to eventually characterize, the nanohertz stochastic gravitational-wave background (SGWB) by looking for correlated deviations in the
pulse times of arrival (TOAs) of multiple radio millisecond pulsars distributed across the sky. The SGWB in the
nanohertz regime is thought to be generated by the incoherent superposition of a large number of weak and unresolved GW sources, including supermassive black hole binaries (SMBHBs) [2–8], decaying cosmic-string networks
[9–12] or primordial GWs [13, 14]. Previous analyses
have assumed background isotropy, which emerges as a
special case from the more general anisotropy framework
presented here. Although GWs have not yet been directly detected, limits on the angular power distribution
of a nanohertz SGWB may constrain the distribution of
low redshift structure [15], the location of several partic-
ularly bright nearby sources dominating the signal strain
budget [16, 17], and open a new avenue to explore the
population characteristics of SMBHBs. Moreover, if a
significant fraction of SMBHBs stall rather than merge,
or are rapidly driven to merger via strong couplings to
the galactic nuclear environment, then we may expect a
depleted nanohertz GW signal dominated by only a few
bright sources [18]. As such, the tools implemented here
may provide new and novel insights into the final-parsec
problem (see e.g. Ref. [19]). This research is a result of the
common effort to directly detect gravitational waves using
pulsar timing, known as the European Pulsar Timing Array
[EPTA, 20].
Limits on the SGWB are usually reported in terms of
the characteristic-strain spectrum hc (f ) of a background
which is composed of purely GW-driven, circular, inspiral-

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