Cosmological dynamics with non-minimally coupled scalar field and

Transcription

arXiv:1507.00654v1 [hep-ph] 2 Jul 2015
The Electroweak Vacuum Angle at Finite
Temperature and Implications for
Baryogenesis
Andrew J. Long,a,∗ Hiren H. Patel,b,† and Mark Troddenc,‡
a Physics
Department and School of Earth and Space Exploration,
Arizona State University, Tempe, Arizona 85287, USA.
b Particle
and Astro-Particle Physics Division, Max-Planck Institut fuer Kernphysik (MPIK)
c Center
for Particle Cosmology, Department of Physics and Astronomy,
University of Pennsylvania, Philadelphia, PA 19104, USA
Abstract
We initiate a study of cosmological implications of sphaleron-mediated CP-violation arising
from the electroweak vacuum angle under the reasonable assumption that the semiclassical
suppression is lifted at finite temperature. In this article, we explore the implications for existing scenarios of baryogenesis. Many compelling models of baryogenesis rely on electroweak
sphalerons to relax a (B + L) charge asymmetry. Depending on the sign of the CP-violating
parameter, it is shown that the erasure of positive (B + L) will proceed more or less quickly
than the relaxation of negative (B + L). This is a higher order effect in the kinetic equation for
baryon number, which we derive here through order n2b+l . Its impact on known baryogenesis
models therefore seems minor, since phenomenologically nb+l is much smaller than the entropy
density. However, there remains an intriguing unexplored possibility that baryogenesis could be
achieved with the vacuum angle alone providing the required CP-violation.
∗
[email protected]
[email protected]
‡
[email protected]
†
Prepared for submission to JCAP
arXiv:1507.00568v1 [gr-qc] 2 Jul 2015
Solar System Constraints on Disformal
Gravity Theories
Hiu Yan Ip,a Jeremy Sakstein,b Fabian Schmidta
a
b
Max-Planck-Institut f¨
ur Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth PO1 3FX, UK
E-mail: [email protected], [email protected],
[email protected]
Abstract. Disformal theories of gravity are scalar-tensor theories where the scalar couples derivatively to matter via the Jordan frame metric. These models have recently attracted interest in the cosmological context since they admit accelerating solutions. We derive the solution for a static isolated
mass in generic disformal gravity theories and transform it into the parameterised post-Newtonian
form. This allows us to investigate constraints placed on such theories by local tests of gravity. The
tightest constraints come from preferred-frame effects due to the motion of the Solar System with
respect to the evolving cosmological background field. The constraints we obtain improve upon the
previous solar system constraints by two orders of magnitude, and constrain the scale of the disformal
coupling for generic models to M & 100 eV. These constraints render all disformal effects irrelevant
for cosmology.
1
arXiv:1507.00531v1 [gr-qc] 2 Jul 2015
A divergence free parametrization of deceleration
parameter for scalar field dark energy
Abdulla Al Mamon1 and Sudipta Das2
Department of Physics, Visva-Bharati,
Santiniketan- 731235, India.
PACS Nos.: 98.80.Hw
Abstract
In this paper, we have considered a spatially flat FRW universe filled with pressureless
matter and dark energy. We have considered a phenomenological parametrization of the
deceleration parameter q(z) and from this we have reconstructed the equation of state for
dark energy ωφ (z). Using the combination of datasets (SN Ia + Hubble + BAO/CMB), we
have constrained the transition redshift zt (at which the universe switches from a decelerating
to an accelerating phase) and have found the best fit value of zt . We have also found that the
reconstructed results of q(z) and ωφ (z) are in good agreement with the recent observations.
The potential term for the present toy model is found to be functionally similar to a Higgs
potential.
Keywords: Cosmic acceleration, Parametrization, Deceleration parameter, Data analysis
1
Introduction
The discovery of the late-time cosmic acceleration [1, 2] opened up a new field of research in modern cosmology. A number of theoretical models have been constructed to explain this accelerated
phenomenon. Most of them are based either on some modification of the Einstein-Hilbert action
[3, 4] or the existence of new kind of exotic fields in nature, dubbed as “dark energy” (DE). In this
paper, we will focus on the second aspect and consider DE as the driving agent for the current accelerated expansion of the universe which is considered as a hypothetical energy component with
a large negative pressure. In the last decade numerous DE models have been explored to account
for this phenomenon (for review, see refs. [5, 6, 7, 8, 9]). In spite of those efforts, however, the
true nature of dark energy still remains a mystery. The most popular and simplest cosmological
DE model is the ΛCDM model, which is in good agreement with the recent observational data.
The ΛCDM model is obtained by introducing a cosmological constant Λ into general relativity,
for which the equation of state parameter ωΛ = −1. However, it suffers from two major problems,
namely, fine tuning and cosmological coincidence problems [10, 11]. This motivates theorists to
1
2
E-mail : [email protected]
E-mail: [email protected]
Dark matter, Mach’s ether and the QCD vacuum
Gilles Cohen-Tannoudjia
Laboratoire de recherche sur les sciences de la matière (LARSIM)
CEA Saclay
Abstract
Here is proposed the idea of linking the dark matter issue (considered as a major problem of contemporary research
in physics) with two other theoretical open questions, one, almost centenary about the existence of an unavoidable
ether in general relativity agreeing with the Mach’s principle, and one, more recent, about the properties of the
quantum vacuum in the quantum field theory of strong interactions, Quantum ChromoDynamics (QCD).
According to this idea, on the one hand dark matter and dark energy, that according to the current standard model
of cosmology, represent about 95% of the universe content can be considered as forming two distinct components
of the Mach’s ether and, on the other hand, dark matter, as a perfect fluid emerging from the QCD vacuum, could
be modeled as a Bose Einstein condensate.
1/ Introduction
The so-called CDM new standard model of cosmology has reached a robustness
level comparable to the one of the standard model of particle physics. However these two
standard models are in conflict about the issue of the dark matter, an outcome of the
cosmological standard model that is a contribution to the balance of cosmological densities,
about five times the one of the ordinary (baryonic) matter, which does not seem to be
explainable in terms of the theories of the particle physics standard model. The purpose of the
present paper is to put in debate the hypothesis that this conflict could be resolved by linking
dark matter with a concept which plays a crucial role in hadronic and nuclear physics, and
belongs to the fundamentals of the standard model of particle physics, namely the QCD
vacuum. Actually, to support this assumption, it appeared useful to revisit an almost centenary
debate about a third concept, the Mach’s ether of general relativity, which led me formulating
my hypothesis in the following way: Mach’s ether, dark matter and QCD vacuum are three
modes of existence of a same entity. The idea is that in a quantum field theory like QCD, what
one calls “vacuum” is the ground state, the state of minimal energy, namely the state in the
Fock space for which all the occupation numbers are zero. But this vacuum is not the
amailto:[email protected]
1
Draft version July 3, 2015
Preprint typeset using LATEX style emulateapj v. 5/2/11
´
SPECTRAL BREAKS OF ALFVENIC
TURBULENCE IN A COLLISIONLESS PLASMA
Stanislav Boldyrev1 , Christopher H. K. Chen2 , Qian Xia1 , Vladimir Zhdankin1
1 Department of Physics, University of Wisconsin–Madison, Madison,
2 Department of Physics, Imperial College London, London SW7
WI 53706, USA
2AZ, UK
(Dated: July 3, 2015)
arXiv:1507.00416v1 [physics.space-ph] 2 Jul 2015
ABSTRACT
Recent observations reveal that magnetic turbulence in the nearly colisionless solar wind plasma
extends to scales smaller than the plasma microscales, such as ion gyroradius and ion inertial length.
Measured breaks in the spectra of magnetic and density fluctuations at high frequencies are thought
to be related to the transition from large-scale hydromagnetic to small-scale kinetic turbulence. The
scales of such transitions and the responsible physical mechanisms are not well understood however.
In the present work we emphasize the crucial role of the plasma parameters in the transition to kinetic
turbulence, such as the ion and electron plasma beta, the electron to ion temperature ratio, the degree
of obliquity of turbulent fluctuations. We then propose an explanation for the spectral breaks reported
in recent observations.
Subject headings: magnetic fields — magnetohydrodynamics — turbulence
1. INTRODUCTION
In situ measurements of the magnetic, electric, and
density fluctuations in the solar wind provide valuable
information on nonlinear dynamics of a nearly collisionless astrophysical plasma. At large hydrodynamic
scales (corresponding to low frequencies in the measurements), such fluctuations are thought to be consistent
with magnetohydrodynamic turbulence viewed as interacting oblique Alfvén modes propagating along the background magnetic field (Iroshnikov 1963; Kraichnan 1965;
Goldreich & Sridhar 1995; Galtier et al. 2000; Boldyrev
2006). At higher frequencies the spectrum of such turbulence exhibits a break, which corresponds to the spatial
scale broadly consistent with the plasma microscales such
as the ion gyroradius or the ion inertial length.
It has been proposed that the spectral break
in the solar wind and other astrophysical plasmas can mark a transition from the non-dispersive
Alfvén modes to the dispersive kinetic-Alfvén
modes (Bale et al. 2005; Leamon et al. 1998, 1999;
Hollweg 1999; Howes et al. 2006; Chandran et al. 2009;
Shaikh & Zank 2009; Chandran et al. 2010; Chen et al.
2010;
Howes & Quataert
2010;
Petrosyan et al.
2010; Howes et al. 2011; Chandran et al. 2011;
TenBarge & Howes 2012; Boldyrev & Perez 2012;
Sahraoui et al.
2012;
Mithaiwala et al.
2012;
Boldyrev & Perez 2013; Podesta 2013; Chen et al.
2013; Haverkorn & Spangler 2013). A possibility of
transition to whistler turbulence has also been considered (Beinroth & Neubauer 1981; Coroniti et al.
1982; Goldstein et al. 1994; Stawicki et al. 2001;
Galtier & Bhattacharjee 2003, 2005; Gary et al. 2008;
Saito et al. 2008; Gary & Smith 2009; Shaikh 2009,
2010; Gary et al. 2010), however, recent studies (e.g.,
Podesta 2013; Chen et al. 2013) suggest that whistler
turbulence, if present at subpropton scales, contributes
only a small fraction of fluctuations energy. A conclusion
is then drawn that the spectral break occurs at the
proton gyroscale.
A recent work by Chen et al. (2014) tested this pre-
diction by analyzing the solar wind intervals having very
large and very small plasma beta, the ratio of the kinetic energy of the plasma particles to the magnetic energy. In particular, the intervals were selected with ion
and electron plasma beta satisfying βi ∼ βe ≫ 1 and
1 ≫ βe ≫ βi . In the first case, the theory of oblique
Alfvénic turbulence predicts the break at the ion gyroscale, in the second one at the ion acoustic scale. The
observations of (Chen et al. 2014) agree with the theory
in the first case, and disagree in the second, where the
break is observed at the ion inertial length instead. This
puzzling result may question the applicability of the theory of turbulent cascade to the solar wind plasma.
We address this contradiction by inspecting the theory
of Alfvén turbulence in the limiting cases of large and
small plasma beta. We consider various mechanisms
that may be responsible for the spectral break, including the possibility that the major assumption of the
standard theory, the obliquity of propagation, can break
down in the case 1 ≫ βe ≫ βi . The reason for the latter
possibility is upscatter of the Alfvénic fluctuations due
to their interactions with the ion-acoustic modes and the
fast modes that are weakly damped in a non-isothermal
low-beta plasma. The Afvénic turbulence then develops
a non-oblique component kk & k⊥ , which is dissipated
due to the ion cyclotron resonance at the ion inertial
scale thus explaining the observed spectral break in this
case.
2. KINETIC DERIVATION
pIn what follows we will use the notation: ωpα =
2
p4πn0α qα /mα is the plasma frequency, and vT α =
Tα /mα is the thermal velocity associated with the particles of kind α. For a plasma consisting of electrons and
ions, the
p so-called ion-acoustic velocity can be defined,
Te /mi . It is also
vs =
√ convenient to introduce the
Alfvén speed vA = B0 / 4πn0 mi , and the plasma beta,
which is the ratio of the thermal energy of the particles
to the magnetic energy of the plasma, and which can be
The I-Q relations for rapidly rotating neutron stars in f ( R) gravity
Daniela D. Doneva,1, 2, ∗ Stoytcho S. Yazadjiev,3, 1, † and Kostas D. Kokkotas1, ‡
1 Theoretical
arXiv:1507.00378v1 [gr-qc] 1 Jul 2015
Astrophysics, Eberhard Karls University of Tubingen,
¨
Tubingen
¨
72076, Germany
2 INRNE - Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria
3 Department of Theoretical Physics, Faculty of Physics, Sofia University, Sofia 1164, Bulgaria
In the present paper we study the behavior of the normalized I-Q relation for neutron stars in a
particular class of f ( R) theories of gravity, namely the R2 gravity that is one of the most natural and
simplest extensions of general relativity in the strong field regime. We study both the slowly and
rapidly rotating cases. The results show that the I-Q relation remain nearly equation of state independent for fixed values of the normalized rotational parameter, but the deviations from universality
can be a little bit larger compared to the general relativistic case. What is the most interesting in our
studies, is that the differences with the pure Einstein’s theory can be large reaching above 20%. This
is qualitative different from the majority of alternative theories of gravity, where the normalized I-Q
relations are almost indistinguishable from the general relativistic case, and can lead to observational
constraints on the f ( R) theories in the future.
PACS numbers:
I.
INTRODUCTION
Studies of generalized theories of gravity are becoming more and more intense in the last decade. There are both
theoretical and observational motivations for this. On one hand the theories trying to unify all the interactions
predict that the standard Einstein-Hilbert action should be modified. On the other hand it was shown in many
cases that studying generalizations of Einstein’s gravity can give us a deeper understanding of general relativity
(GR) itself. On the observational front still remain phenomena that do not fit very well in the standard framework,
such as the accelerated expansion of the universe, and that is why modifications of the theory of gravity are often
employed as an alternative explanations. One should keep also in mind, that even though general relativity is very
well tested in the weak field regime, the strong field remains essentially unconstrained that leaves space for a variety
of modifications.
One of the most natural generalizations of Einstein’s theory of gravity are the f ( R) theories, where the Ricci scalar
R in the Einstein-Hilbert action is replaced by some function of R. Such modification has a theoretical motivation for
example from the quantum field theory in curved spacetime. f ( R) theories are also widely used as an alternative
explanation of the dark energy phenomena which places them amongst the most popular and widely explored
alternative theories of gravity. Most of the studies on f ( R) theories though are in cosmological aspect in relation
to the accelerated expansion of the universe [1–3]. The examinations of the astrophysical manifestations of these
theories is more scarce and this would be the main focus of our paper.
Natural objects to study within the f ( R) theories of gravity at astrophysical scales are the neutron stars, where
the strong gravity effects are non-negligible. The neutron stars within the f ( R) theories can differ significantly from
their GR counterpart [4–6] which makes them a very good candidate to test f ( R) theories on astrophysical scales.
Unfortunately one has to pay a high price – the nuclear matter equation of state (EOS) at densities as high as the ones
in the neutron star cores, is still unknown. That is why in many cases the deviations coming from the generalizations
of Einstein’s gravity are comparable or even smaller than the deviations resulting from the uncertainties in the EOS.
A way to circumvent this problem is to search for predictions or derive relations that are independent of the EOS.
This was exactly the idea in [7, 8] where the famous I-Love-Q relations were discovered. These relations connect the
∗ Electronic
address: [email protected]
‡ Electronic address: [email protected]
† Electronic
DRAFT: July 3, 2015
PHYSICAL PROPERTIES OF A PILOT SAMPLE OF SPECTROSCOPIC CLOSE PAIR GALAXIES AT Z ∼ 2
David R. Law1 , Alice E. Shapley2 , Jade Checlair3 , Charles C. Steidel4
arXiv:1507.00721v1 [astro-ph.GA] 2 Jul 2015
DRAFT: July 3, 2015
ABSTRACT
We use Hubble Space Telescope Wide-Field Camera 3 (HST/WFC3) rest-frame optical imaging to
select a pilot sample of star-forming galaxies in the redshift range z = 2.00 − 2.65 whose multicomponent morphologies are consistent with expectations for major mergers. We follow up this
sample of major merger candidates with Keck/NIRSPEC longslit spectroscopy obtained in excellent
seeing conditions (FWHM ∼ 0.5 arcsec) to obtain Hα-based redshifts of each of the morphological
components in order to distinguish spectroscopic pairs from false pairs created by projection along
the line of sight. Of six pair candidates observed, companions (estimated mass ratios 5:1 and 7:1)
are detected for two galaxies down to a 3σ limiting emission-line flux of ∼ 10−17 erg s−1 cm−2 .
This detection rate is consistent with a ∼ 50% false pair fraction at such angular separations (1 − 2
arcsec), and with recent claims that the star-formation rate (SFR) can differ by an order of magnitude
between the components in such mergers. The two spectroscopic pairs identified have total SFR, SFR
surface densities, and stellar masses consistent on average with the overall z ∼ 2 star forming galaxy
population.
Subject headings: galaxies: fundamental parameters — galaxies: high-redshift — galaxies: structure
1. INTRODUCTION
At redshift z ∼ 2 − 3 galaxies are growing rapidly
and build up a large fraction of their present-day
stellar mass (e.g. Reddy et al. 2008). As they grow,
the increased stellar mass is thought to stabilize
these systems against gravitational instabilities resulting from their large gas fractions (e.g., Kassin et al.
2014; van der Wel et al. 2014), decreasing their formerlyhigh gas-phase velocity dispersions (Law et al. 2007b,
2009; Förster Schreiber et al. 2009; Newman et al. 2013)
and causing a morphological transformation from highlyirregular clumpy starbursts (e.g., Guo et al. 2012;
Law et al. 2012a; van der Wel et al. 2014, and references therein) to the modern-day Hubble sequence (e.g.,
Papovich et al. 2005; Law et al. 2012b; Conselice 2014).
One mechanism by which such growth occurs is the
conversion of massive gas reservoirs into stars. Such
star formation is observed to occur at a typical rate
∼ 30M⊙ yr−1 for rest-UV selected galaxy samples (e.g.,
Erb et al. 2006; Wuyts et al. 2011), although this SFR
may represent only a small fraction of the gas continually cycling into (e.g., Genzel et al. 2008; Dekel et al.
2009) and out of the galaxies (e.g., Steidel et al. 2010)
through large-scale gas flows. Likewise, galaxies also
grow through both major (mass ratio 3 : 1 or lower)
and minor (mass ratio 4 : 1 or higher) mergers with
other galaxies. Such events typically contribute both
stars and gas, thereby building up the galactic stellar
spheroid population and providing fuel for future generations of star formation. The role of mergers and merger1 Space Telescope Science Institute, 3700 San Martin Drive,
Baltimore, MD 21218, USA ([email protected])
2 Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA
3 Dunlap Institute for Astronomy & Astrophysics, University
of Toronto, 50 St. George Street, Toronto M5S 3H4, Ontario,
Canada
4 California Institute of Technology, MS 249-17, Pasadena, CA
91125, USA
induced star formation compared to in-situ star formation in building up the present day galaxy population
has been the subject of considerable debate, with various
studies claiming both that mergers are (de Ravel et al.
2009; Puech et al. 2014; Tasca et al. 2014) and are not
(Shapiro et al. 2008; Williams et al. 2011; Wuyts et al.
2011; Kaviraj et al. 2013) major drivers of star formation and galactic stellar mass assembly since z ∼ 4.
Significant effort has therefore been invested both in
constraining the evolution of the merger fraction for
star-forming galaxies (e.g., Conselice et al. 2008, 2011;
Lotz et al. 2008, 2011; Rawat et al. 2008) and in assessing the physical effects of such mergers on the star formation properties of the galaxies (e.g., Law et al. 2007a,
2012a; Lotz et al. 2008; Lee et al. 2013). One method
employed by such studies is to use high-resolution
imaging to quantify disturbances and irregularities in
the surface brightness profile using a variety of nonparametric indices (e.g., Conselice et al. 2000; Lotz et al.
2004; Law et al. 2007a). However, it is often challenging
to intepret such indices unambiguously because z ∼ 2 − 3
galaxies are intrinsically clumpy and irregular and similar disturbed morphologies can arise both in merging
systems and in isolated star forming galaxies due to internal dynamical instabilities (e.g., Bournaud & Elmegreen
2009; Genzel et al. 2011).
An alternative way of identifying major mergers is to
look for close angular pairs (r . 50 kpc, 6 arcsec at
z ∼ 2−3). When the velocity separation between the two
components in such a pair is . 500 km s−1 (see discussion by Lin et al. 2004; Lotz et al. 2008) numerical simulations suggest that such systems should predominantly
trace major galaxy-galaxy mergers during their first pericentric passage and before final coalescence (Lotz et al.
2008, 2010). Indeed, when merger rates derived from
such close pairs (e.g., Bundy et al. 2009; Williams et al.
2011; de Ravel et al. 2009; L´
opez-Sanjuan et al. 2013;
Tasca et al. 2014) are combined with physically moti-
arXiv:1507.00718v1 [astro-ph.CO] 2 Jul 2015
CMB and BAO constraints for an
induced gravity dark energy model
with a quartic potential
C. Umiltàa,b,c M. Ballardinid,e,f F. Finellie,f and D. Paolettie,f
a Institut
d’Astrophysique de Paris, CNRS (UMR7095), 98 bis Boulevard Arago, F-75014,
Paris, France
b UPMC Univ Paris 06, UMR7095, 98 bis Boulevard Arago, F-75014, Paris, France
c Sorbonne Universités, Institut Lagrange de Paris (ILP), 98 bis Boulevard Arago, 75014
Paris, France
d DIFA, Dipartimento di Fisica e Astronomia, Via Berti Pichat, I-40129 Bologna, Italy
e INAF-IASF Bologna, via Gobetti 101, I-40129 Bologna, Italy
f INFN, Sezione di Bologna, Via Irnerio 46, I-40126 Bologna, Italy
E-mail: [email protected], [email protected], [email protected],
[email protected]
Abstract. We study the predictions for structure formation in an induced gravity dark energy
model with a quartic potential. By developing a dedicated Einstein-Boltzmann code, we study
self-consistently the dynamics of homogeneous cosmology and of linear perturbations without
using any parametrization. By evolving linear perturbations with initial conditions in the
radiation era, we accurately recover the quasi-static analytic approximation in the matter
dominated era. We use Planck 2013 data and a compilation of baryonic acoustic oscillation
(BAO) data to constrain the coupling γ to the Ricci curvature and the other cosmological
parameters. By connecting the gravitational constant in the Einstein equation to the one
measured in a Cavendish-like experiment, we find γ < 0.0012 at 95% CL with Planck 2013
and BAO data. This is the tightest cosmological constraint on γ and on the corresponding
derived post-Newtonian parameters. Because of a degeneracy between γ and the Hubble
constant H0 , we show how larger values for γ are allowed, but not preferred at a significant
statistical level, when local measurements of H0 are combined in the analysis with Planck
2013 data.
CONNECTING THE DOTS: TRACKING GALAXY EVOLUTION USING CONSTANT CUMULATIVE
NUMBER DENSITY AT 3 ≤ z ≤ 7
Jason Jaacks1 ∗, Steven L. Finkelstein1 & Kentaro Nagamine2,3
1 Department
of Astronomy, The University of Texas at Austin, Austin, TX 78712
of Earth and Space Science, Graduate School of Science, Osaka University,
1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
3 Department of Physics & Astronomy, University of Nevada, Las Vegas,
4505 S. Maryland Pkwy, Las Vegas, NV, 89154-4002, USA
2 Department
ABSTRACT
Using the cosmological smoothed particle hydrodynamical code GADGET-3 we make a realistic
assessment of the technique of using constant cumulative number density as a tracer of galaxy evolution
at high redshift. We find that over a redshift range of 3 ≤ z ≤ 7 one can on average track the growth
of the stellar mass of a population of galaxies selected from the same cumulative number density bin
to within ∼ 0.20 dex. Over the stellar mass range we probe (1010.39 ≤ Ms /M ≤ 1010.75 at z =
3 and 108.48 ≤ Ms /M ≤ 109.55 at z = 7) one can reduce this bias by selecting galaxies based on
an evolving cumulative number density. We find the cumulative number density evolution exhibits a
trend towards higher values which can be quantified by simple linear formulations going as −0.10∆z
for descendants and 0.12∆z for progenitors. Utilizing such an evolving cumulative number density
increases the accuracy of descendant/progenitor tracking by a factor of ∼ 2. This result is in excellent
agreement, within 0.10 dex, with abundance matching results over the same redshift range. However,
we find that our more realistic cosmological hydrodynamic simulations produce a much larger scatter
in descendant/progenitor stellar masses than previous studies, particularly when tracking progenitors.
This large scatter makes the application of either the constant cumulative number density or evolving
cumulative number density technique limited to average stellar masses of populations only, as the
diverse mass assembly histories caused by stochastic physical processes such as gas accretion, mergers,
and star formation of individual galaxies will lead to a larger scatter in other physical properties such
as metallicity and star-formation rate.
Subject headings: cosmology: theory — stars: formation — galaxies: evolution – galaxies: formation
– methods: numerical
1. INTRODUCTION
Understanding how galaxies evolved from minute perturbations in the distant Universe into the diverse zoo of
shapes and sizes we see today is one of the fundamental goals of modern astronomy. The current frontier lies
at the edge of the observable universe, ∼ 500 Myr after
the Big Bang, and is primarily possible using the Wide
Field Camera 3 (WFC3) instrument aboard the Hubble Space Telescope (HST). Using the Lyman-break technique and/or photometric redshifts to select candidate
galaxies, programs such as CANDELS (PIs Faber & Ferguson), BoRG (Trenti et al. 2011), and HUDF09/UDF12
(Bouwens et al. 2011; Ellis et al. 2013), are able to
identify galaxies down to rest-frame UV magnitudes of
Muv ∼ −17.5 (e.g., Finkelstein et al. 2012, 2014; Trenti
et al. 2011; Bouwens et al. 2012; Ellis et al. 2013). Two
of these galaxies have been spectroscopically confirmed
to be the earliest known galaxies to date with redshifts
of z=7.51 (Finkelstein et al. 2013) and z=7.73 (Oesch
et al. 2015). With the help of the gravitational lensing
effect of massive foreground galaxy clusters, campaigns
such as CLASH (Bouwens et al. 2014) and the HST Frontier Fields will extend our understanding even further to
z ≥ 9 and UV magnitudes as faint as Muv ∼ −13, greatly
increasing the dynamic range of the observed galaxy pop* [email protected]
ulation for study.
From these surveys, fundamental properties such as
stellar mass, age and star formation rate (SFR) can be
derived by comparing the spectral energy distributions
(SEDs) of galaxies to stellar population models. By selecting galaxies at different epochs (“snapshots” in time),
we can in principle directly observe how galaxies evolve.
However, tracing galaxies from one epoch to another has
proven challenging, and frequently accompanied by misinterpretation. Previous studies have matched galaxies
at different epochs by comparing samples selected to have
similar physical tracers, such as a constant stellar mass
or SFR (e.g., Stark et al. 2009). This can be problematic as two galaxies, one at z=6 and the other at z=3,
both with stellar masses of M∗ ≈ 1010 M could have
dramatically different mass assembly histories depending on their individual star formation histories (SFHs),
environments and/or merger histories.
A novel approach to this problem was suggested by van
Dokkum et al. (2010) who tracked a population of galaxies through cosmic time (z=2 to z=0.1) selected to have
a constant number density, using the observed cumulative galaxy stellar mass function (CSMF). The critical
assumption this approach makes is that galaxies in the
same number density bin will grow at a similar, smooth
rate with a conserved rank order. Monte Carlo simulations were utilized to test the effects of mergers and
MNRAS 000, 1–6 (2008)
Preprint 3 July 2015
Hyperfine transitions of
13
Compiled using MNRAS LATEX style file v3.0
CN from pre-protostellar sources
D. R. Flower1⋆ , P. Hily-Blant2
1 Physics
2 LAOG
Department, The University, Durham DH1 3LE, UK
(UMR 5571), Universit´
e de Grenoble, BP 53, F-38041 Grenoble Cedex 09, France
Accepted 2008 December 15. Received 2008 December 14; in original form 2008 October 11
ABSTRACT
Recent quantum mechanical calculations of rate coefficients for collisional transfer
of population between the hyperfine states of 13 CN enable their population densities
to be determined. We have computed the relative populations of the hyperfine states
of the N = 0, 1, 2 rotational states for kinetic temperatures 5 6 T 6 20 K and
molecular hydrogen densities 1 6 n(H2 ) 6 1010 cm−3 . Spontaneous and induced
radiative transitions were taken into account. Our calculations show that, if the lines
are optically thin, the populations of the hyperfine states, F , within a given rotational
manifold are proportional to their statistical weights, (2F + 1) – i.e. in LTE – over the
entire range of densities. We have re-analyzed IRAM 30 m telescope observations of
13
CN hyperfine transitions (N = 1 → 0) in four starless cores. A comparison of these
observations with our calculations confirms that the hyperfine states are statistically
populated in these sources.
Key words:
ISM: molecules – molecular processes – submillimetre: ISM – stars: low-mass.
1
INTRODUCTION
The interpretation of the emission lines of molecules in the
interstellar medium (ISM) is often complicated by the effects of re-absorption and scattering, owing to significant
optical depths in the lines. Partly for this reason, observations of less abundant isotopologues are analyzed, in addition or in preference to those of the principal species; this
is the case of CO, for example, where 13 CO and C18 O lines
are used, and also of CN, where 13 CN and C15 N serve a
similar purpose. In the present paper, we consider the emission lines of 13 CN, observed at millimetre wavelengths in
pre-protostellar sources.
13
CN has a rich spectrum at mm-wavelengths, where
it displays the effects of the fine structure interaction, between the electron spin and the nuclear rotation, and of the
hyperfine interaction with the spins of the 13 C (I1 = 21 ) and
N (I2 = 1) nuclei. Thus, Bogey et al. (1984) listed 16 ‘allowed’ transitions, in the vicinity of 100 GHz, between the
rotational states N = 0 and N = 1, and a further 25 transitions at 200 GHz between the N = 1 and N = 2 states. It is
this cornucopia of optically thin transitions that one wishes
to exploit, in order to obtain a better understanding of the
conditions in pre-protostellar objects.
It is generally assumed that the hyperfine levels, F , of
⋆
c 2008 The Authors
a given N are populated in proportion to their statistical
weights, (2F + 1), i.e. that they are in local thermodynamic
equilibrium LTE. However, LTE is the exception, rather
than the rule, in the ISM, because very low densities prevail. The assumption of LTE is usually dictated by a lack of
rate coefficients for collisional population transfer between
the hyperfine levels of the molecule. In the case of 13 CN
(and of C15 N), this situation has been rectified recently by
the calculations of Flower & Lique (2015), which provide
rate coefficients for collisions with para-H2 in its rotational
ground state – the dominant perturber at low kinetic temperatures, T . Thus, the opportunity arises to calculate the
hyperfine level populations explicitly, allowing for collisional
and radiative transfer, where the latter is induced by the
cosmic microwave background or by the emission of dust
present in the medium.
We present the details of the calculations in Section 2
and the numerical results and their implications in the following Section 3. Our concluding remarks are in Section 4.
2
CALCULATIONS
Bogey et al. (1984) note that the rotational (N ) and the
hyperfine (F ) are the ‘good’ quantum numbers of 13 CN.
Accordingly, we evaluate the relative populations, in equilibrium, of the levels (N, F ), for a wide range of values of
Version from July 3, 2015
arXiv:1507.00708v1 [astro-ph.SR] 2 Jul 2015
On Infrared Excesses Associated With Li-Rich K Giants
Luisa M. Rebull1 , Joleen K. Carlberg2,3, John C. Gibbs4 , J. Elin Deeb5 , Estefania Larsen6 , David V.
Black7 , Shailyn Altepeter6 , Ethan Bucksbee6 , Sarah Cashen4 , Matthew Clarke6, Ashwin Datta4 , Emily
Hodgson4 , Megan Lince4
ABSTRACT
Infrared (IR) excesses around K-type red giants (RGs) have previously been discovered using
Infrared Astronomy Satellite (IRAS) data, and past studies have suggested a link between RGs
with overabundant Li and IR excesses, implying the ejection of circumstellar shells or disks.
We revisit the question of IR excesses around RGs using higher spatial resolution IR data,
primarily from the Wide-field Infrared Survey Explorer (WISE). Our goal was to elucidate the
link between three unusual RG properties: fast rotation, enriched Li, and IR excess. Our sample
of RGs includes those with previous IR detections, a sample with well-defined rotation and Li
abundance measurements with no previous IR measurements, and a large sample of RGs asserted
to be Li-rich in the literature; we have 316 targets thought to be K giants, about 40% of which
we take to be Li-rich. In 24 cases with previous detections of IR excess at low spatial resolution,
we believe that source confusion is playing a role, in that either (a) the source that is bright in
the optical is not responsible for the IR flux, or (b) there is more than one source responsible for
the IR flux as measured in IRAS. We looked for IR excesses in the remaining sources, identifying
28 that have significant IR excesses by ∼20 µm (with possible excesses for 2 additional sources).
There appears to be an intriguing correlation in that the largest IR excesses are all in Li-rich
K giants, though very few Li-rich K giants have IR excesses (large or small). These largest IR
excesses also tend to be found in the fastest rotators. There is no correlation of IR excess with
the carbon isotopic ratio, 12 C/13 C. IR excesses by 20 µm, though relatively rare, are at least
twice as common among our sample of Li-rich K giants. If dust shell production is a common
by-product of Li enrichment mechanisms, these observations suggest that the IR excess stage is
very short-lived, which is supported by theoretical calculations. Conversely, the Li-enrichment
mechanism may only occasionally produce dust, and an additional parameter (e.g., rotation) may
control whether or not a shell is ejected.
Subject headings: stars: late-type; stars:evolution; infrared:stars
1 Spitzer
Science Center (SSC) and Infrared Science Archive (IRSA), Infrared Processing and Analysis Center (IPAC), 1200
E. California Blvd., California Institute of Technology, Pasadena, CA 91125 USA; [email protected]
2 NASA
Goddard Space Flight Center, Code 667, Greenbelt MD 20771 USA
3 NASA
Postdoctoral Program Fellow
4 Glencoe
5 Bear
High School, 2700 NW Glencoe Rd., Hillsboro, OR 97124 USA
Creek High School, 9800 W. Dartmouth Pl., Lakewood, CO 80227 USA
6 Millard
South High School, 14905 Q St., Omaha, NE 68137 USA
7 Walden
School of Liberal Arts, 4230 N. University Ave., Provo, UT 84604 USA
Acta Polytechnica 00(0):1–12, 0000
© Czech Technical University in Prague, 2015
PREPRINT 2015-07-03
GALACTIC CENTER MINISPIRAL: INTERACTION MODES OF
NEUTRON STARS
Michal Zajačeka,b,c,d,∗ , Vladimír Karasc , Devaky Kunneriathc
a
I. Physikalisches Institut der Universität zu Köln, Zülpicher Strasse 77, D-50937 Köln, Germany
b
Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, D-53121 Bonn, Germany
c
Astronomical Institute, Academy of Sciences, Boční II 1401, CZ-14131 Prague, Czech Republic
d
Charles University in Prague, Faculty of Mathematics and Physics, V Holešovičkách 2, CZ-18000 Prague,
Czech Republic
∗
corresponding author: [email protected]
Abstract. Streams of gas and dust in the inner parsec of the Galactic center form a distinct feature
known as the Minispiral, which has been studied in radio waveband as well as in the infrared wavebands.
A large fraction of the Minispiral gas is ionized by radiation of OB stars present in the Nuclear Star
Cluster (NSC). Based on the inferred mass in the innermost parsec (∼ 106 solar masses), over ∼ 103
– 104 neutron stars should move in the sphere of gravitational influence of the SMBH. We estimate
that a fraction of them propagate through the denser, ionized medium concentrated mainly along the
three arms of the Minispiral. Based on the properties of the gaseous medium, we discuss different
interaction regimes of magnetised neutron stars passing through this region. Moreover, we sketch
expected observational effects of these regimes. The simulation results may be applied to other galactic
nuclei hosting NSC, where the expected distribution of the interaction regimes is different across
different galaxy types.
Keywords: Galaxy: center, ISM: individual objects (Sagittarius A), Stars: neutron.
1. Introduction
The Galactic center hosts the supermassive black hole
(SMBH) observed as the compact radio source Sgr A*,
which is surrounded by the Nuclear star cluster (NSC)
and gaseous-dusty structures, such as HII Minispiral
arms of Sgr A West, supernova remnant Sgr A East,
molecular clouds, and the Circumnuclear disk [1, 2].
It is the closest SMBH and hence its environment
can be studied with the highest resolution among
galactic nuclei in the radio-, mm-, submm-, infrared,
and X-ray wavebands [2]. However, despite highresolution multiwavelength studies several processes
are still not satisfactorily explained, such as the starformation near the SMBH, the feeding and feedback
of Sgr A*, and the distribution of the magnetic field
and its interaction with other stellar and non-stellar
components.
The observations of the Galactic center region revealed a large population of young massive stars orbiting the SMBH as close as ∼ 0.1 pc [3]. In fact, the
NSC seems to be one of the densest concentrations
of young massive stars in the Galaxy [1]. On the
other hand, there is an observable flat distribution of
late-type stars with a radius of as much as 1000 [4, 5].
Thus, a steep relaxed Bahcall-Wolf cusp of stars with
a slope of 7/4 or 3/2 [6, 7] is probably absent [5, 8].
The estimates of the number of stellar remnants
that use the power-law initial mass function (IMF)
(standard Salpeter or top-heavy) combined with the
mass segregation over the age of the bulge (∼ 10 Gyr)
lead to a considerable population of stellar black holes
of the order of ∼ 104 [9–11]. The same order is expected for neutron stars based on multiwavelength
statistical studies [12]. Based on the total X-ray luminosity of the innermost parsec, [13] set an upper limit
on the number of compact remnants (. 40 000).
Such an abundant population of neutron stars exhibiting strong magnetic fields could be utilized to
further extend our knowledge about the processes in
the Galactic center. The observations of neutron stars
(pulsars as well as X-ray sources) near the SMBH
would contribute to:
• our understanding of the star formation processes
near the Galactic center using the number and the
age distribution of observed sources,
• mapping the gravitational potential near the SMBH
using their period derivatives,
• constraining the electron density profile in the
Galactic center using their dispersion measures.
Despite continuing efforts only very few pulsars
have been detected in the broader Galactic center
region. It is thought that the lack of detections is
due to profound interstellar dispersion and scattering.
However, there are observational hints that such a
population is present. [14] report the discovery of two
highly dispersed pulsars with the angular separation
. 0.3◦ from the Galactic center. [15] confirm the detection of three pulsars with large dispersion measures
with an offset of ∼ 100 –150 from Sgr A*. There is an
1
CHANG-ES V:
Nuclear Radio Outflow in a Virgo Cluster Spiral after a Tidal
Disruption Event
Judith A. Irwin1 , Richard N. Henriksen1 , Marita Krause2 , Q. Daniel Wang3 , Theresa
Wiegert1 , Eric J. Murphy4 , George Heald5 , and Eric Perlman6
ABSTRACT
We have observed the Virgo Cluster spiral galaxy, NGC 4845, at 1.6 and 6 GHz using the
Karl G. Jansky Very Large Array, as part of the ‘Continuum Halos in Nearby Galaxies – an
EVLA Survey’ (CHANG-ES). The source consists of a bright unresolved core with a surrounding
weak central disk (1.8 kpc diameter). The core is variable over the 6 month time scale of the
CHANG-ES data and has increased by a factor of ≈ 6 since 1995. The wide bandwidths of
CHANG-ES have allowed us to determine the spectral evolution of this core which peaks between
1.6 and 6 GHz (it is a GigaHertz-peaked spectrum source). We show that the spectral turnover
is dominated by synchrotron self-absorption and that the spectral evolution can be explained by
adiabatic expansion (outflow), likely in the form of a jet or cone. The CHANG-ES observations
serendipitously overlap in time with the hard X-ray light curve obtained by Nikolajuk & Walter
(2013) which they interpret as due to a tidal disruption event (TDE) of a super-Jupiter mass
object around a 105 M black hole. We outline a standard jet model, provide an explanation for
the observed circular polarization, and quantitatively suggest a link between the peak radio and
peak X-ray emission via inverse Compton upscattering of the photons emitted by the relativistic
electrons. We predict that it should be possible to resolve a young radio jet via VLBI as a result
of this nearby TDE.
Subject headings: galaxies: individual (NGC 4845) — galaxies: active — galaxies: jets — galaxies: nuclei
1.
Introduction
1 Dept.
of Physics, Engineering Physics, & Astronomy,
Queen’s University, Kingston, Ontario, Canada, K7L 3N6
[email protected], [email protected],
[email protected] .
2 Max-Planck-Institut
f¨
ur
Radioastronomie,
Auf dem H¨
ugel 69,
53121,
Bonn,
Germany,
[email protected].
3 Dept.
of Astronomy, University of Massachusetts,
710 North Pleasant St., Amherst, MA, 01003, USA,
[email protected].
4 US Planck Data Center, The California Institute
of Technology, MC 220-6, Pasadena, CA, 91125, USA,
[email protected].
5 Netherlands Institute for Radio Astronomy (ASTRON), Postbus 2, 7990 AA, Dwingeloo, The Netherlands,
[email protected].
6 Physics and Space Sciences Dept., Florida Institute of
Technology, 150 West University Boulevard, Melbourne,
FL, 32901, USA, [email protected].
The discovery of a hard X-ray source at the
center of the galaxy, NGC 4845, by INTEGRAL
(IGRJ12580+0134) has been interpreted as the
tidal disruption of a super-Jupiter by a massive
black hole (Nikolajuk & Walter 2013). As part
of the Continuum Halos in Nearby Galaxies –
an EVLA1 Survey (CHANG-ES), we have detected a variable radio source (a compact core)
in NGC4845 (Table 1), showing unambiguously
that this galaxy harbours an active galactic nucleus (AGN). The peak of the X-ray light curve
occurred on January 22, 2011. Our radio observations were carried out approximately one year
1 The
Expanded Very Large Array is now known as the Jansky Very Large Array.
1
CHARGE OF INTERSTELLAR DUST IN DENSE MOLECULAR CLOUDS: EFFECT OF COSMIC RAYS
A. V. Ivlev1 , M. Padovani2,3 , D. Galli3 , and P. Caselli1
2
1 Max-Planck-Institut
f¨
ur Extraterrestrische Physik, 85741 Garching, Germany
Laboratoire Univers et Particules de Montpellier, UMR 5299 du CNRS, Universit´
e de Montpellier, 34095 Montpellier, France
3 INAF-Osservatorio Astrofisico di Arcetri, 50125 Firenze, Italy
ABSTRACT
The local cosmic-ray (CR) spectra are calculated for typical characteristic regions of a cold dense
molecular cloud, to investigate two so far neglected mechanisms of dust charging: collection of
suprathermal CR electrons and protons by grains, and photoelectric emission from grains due to the
UV radiation generated by CRs. The two mechanisms add to the conventional charging by ambient
plasma, produced in the cloud by CRs. We show that the CR-induced photoemission can dramatically
modify the charge distribution function for submicron grains. We demonstrate the importance of the
obtained results for dust coagulation: While the charging by ambient plasma alone leads to a strong
Coulomb repulsion between grains and inhibits their further coagulation, the combination with the
photoemission provides optimum conditions for the growth of large dust aggregates in a certain region
of the cloud, corresponding to the densities n(H2 ) between ∼ 104 cm−3 and ∼ 106 cm−3 . The charging
effect of CR is of generic nature, and therefore is expected to operate not only in dense molecular
clouds but also in the upper layers and the outer parts of protoplanetary discs.
Subject headings: ISM: dust – ISM: clouds – ISM: cosmic rays
1. INTRODUCTION
Interstellar dust grains in dense molecular clouds
are subject to several electric charging processes
(e.g., Draine & Salpeter 1979; Draine & Sutin 1987;
Weingartner & Draine 2001b). The resulting net electric
charge carried by micron or sub-micron size grains has
important consequences for the chemical and dynamical
evolution of molecular clouds: it affects the process of
dust coagulation (Okuzumi 2009; Dominik et al. 2007),
the rate of grain-catalyzed electron-ion recombination
(Mestel & Spitzer 1956; Watson 1974), the amount of
gas-phase elemental depletion (Spitzer 1941), and the
electrical resistivity of the cloud’s plasma (Elmegreen
1979; Wardle & Ng 1999). The resistivity, in turn, controls the coupling between the neutral gas and the interstellar magnetic field, and eventually the dynamics of
gravitational collapse of molecular clouds and the formation of stars (e.g., Nakano et al. 2002; Shu et al. 2006).
Collisions of dust grains with the plasma of thermal
electrons and ions from the gas (hereafter, cold plasma
charging) represent an important dust charging process
in molecular clouds (e.g., Draine & Sutin 1987; Draine
2011). Since electrons of mass me have a thermal speed
which is much
p larger than that of ions of mass mi (by
the factor mi /me ≫ 1), grains acquire by this process a (predominantly) negative charge. The photoelectric effect (also called photoemission), on the other
hand, results in positive charging of dust grains, and
is set by the radiation field in the cloud at energies
above a few eV. Photoemission is an important charging process for diffuse gas with visual extinction AV .
10 (e.g., Bakes & Tielens 1994; Weingartner & Draine
2001b). As the interstellar radiation field is exponentially attenuated with increasing AV , photoemission is
usually neglected to compute the charge distribution of
e-mail: [email protected]
grains in the dense gas of molecular cloud cores (e.g.,
Umebayashi & Nakano 1980; Nishi et al. 1991).
Cold plasma charging and photoemission are usually
assumed to be the dominant grain charging mechanisms
in the cold interstellar medium. In this paper we study
the effects of cosmic rays (CRs) on the charging of submicron dust grains in molecular clouds. We focus on
two charging processes that contribute in addition to
the cold-plasma charging, but have been completely neglected so far. By calculating the local CR spectra for
typical cloud regions, we investigate the effects of (i)
collection of suprathermal CR electrons and protons by
grains and (ii) photoelectric emission from grains due
to the UV radiation generated by CRs. Using the coldplasma collection as the “reference case”, we show that
the photoelectric emission can dramatically modify the
charge distribution function for dust in almost the entire cloud, and discuss important implications of the obtained results. In particular, we point out that while the
cold-plasma charging alone leads to a strong Coulomb
repulsion between grains and inhibits their further coagulation, the combination with the CR-induced photoemission provides optimum conditions for the growth of
large dust aggregates in a certain region of the cloud.
2. CR PROPERTIES RELEVANT TO DUST CHARGING
The specific intensities (or spectra) of CR protons and
electrons inside a dense molecular cloud are determined
by the interstellar CR spectra. In order to constrain
the trend of the interstellar spectra at high energies
(E & 500 MeV), we use the latest results of the Alpha Magnetic Spectrometer (AMS-02), mounted on the
International Space Station (Aguilar et al. 2014, 2015).
The high-energy spectrum slope is −3.2 for electrons,
while for protons it is −2.7.
At lower energies, the shape of the interstellar CR spectrum is highly uncertain due to the effect of Solar mod-
The Wide Area VISTA Extra-galactic Survey
(WAVES)
Simon P. Driver, Luke J. Davies, Martin Meyer, Chris Power, Aaron S.G.
Robotham, Ivan K. Baldry, Jochen Liske and Peder Norberg
Abstract The “Wide Area VISTA Extra-galactic Survey” (WAVES) is a 4MOST
Consortium Design Reference Survey which will use the VISTA/4MOST facility
to spectroscopically survey ∼ 2 million galaxies to rAB < 22 mag. WAVES consists
of two interlocking galaxy surveys (“WAVES-Deep” and “WAVES-Wide”), providing the next two steps beyond the highly successful 1M galaxy Sloan Digital Sky
Survey and the 250k Galaxy And Mass Assembly survey. WAVES will enable an
unprecedented study of the distribution and evolution of mass, energy, and structures
extending from 1-kpc dwarf galaxies in the local void to the morphologies of 200Mpc filaments at z ∼ 1. A key aim of both surveys will be to compare comprehensive
empirical observations of the spatial properties of galaxies, groups, and filaments,
against state-of-the-art numerical simulations to distinguish between various Dark
Matter models.
1 Introduction
Since the pioneering days of the 2dFGRS and SDSS, extra-galactic spectroscopic
surveys have come in two flavours: those optimised for cosmology, and those optiSimon P. Driver, Luke J. Davies, Martin Meyer, Chris Power, Aaron S.G. Robotham
International Centre for Radio Astronomy Research (ICRAR), School of Physics, University of
Western Australia, M468, 35 Stirling Highway, Crawley, Western Australia, WA 6009 e-mail:
[email protected]
Ivan K.Baldry
Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park,
146 Brownlow Hill Liverpool, L3 5RF, UK
Jochen Liske
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748, Garching, Germany
Peder Norberg
International Cosmology Centre, Durham University, Durham, DH1 3LE, UK
1
Mon. Not. R. Astron. Soc. 000, 1–?? ()
Printed 3 July 2015
(MN LATEX style file v2.2)
A giant ring-like structure at 0.78 < z < 0.86 displayed by
GRBs
L. G. Balázs1,2⋆ , Z. Bagoly2,3, J. E. Hakkila4, I. Horváth3, J. Kóbori2,
I. Rácz1, L. V. Tóth2
1 MTA
CSFK Konkoly Observatory, Konkoly-Thege M. u
´t 13-17, Budapest, 1121, Hungary
University, P´
azm´
any P´
eter s´
et´
any 1/A, Budapest,1117, Hungary
3 National University of Public Service, 1083, Budapest, Hungary
4 Department of Physics and Astronomy, The College of Charleston, Charleston, SC 29424-0001, USA
2 E¨
otv¨
os
ABSTRACT
According to the cosmological principle, Universal large-scale structure is homogeneous and isotropic. The observable Universe, however, shows complex structures even
on very large scales. The recent discoveries of structures significantly exceeding the
transition scale of 370 Mpc pose a challenge to the cosmological principle.
We report here the discovery of the largest regular formation in the observable
Universe; a ring with a diameter of 1720 Mpc, displayed by 9 gamma ray bursts
(GRBs), exceeding by a factor of five the transition scale to the homogeneous and
isotropic distribution. The ring has a major diameter of 43o and a minor diameter of
30o at a distance of 2770 Mpc in the 0.78 < z < 0.86 redshift range, with a probability
of 2 × 10−6 of being the result of a random fluctuation in the GRB count rate.
Evidence suggests that this feature is the projection of a shell onto the plane of the
sky. Voids and string-like formations are common outcomes of large-scale structure.
However, these structures have maximum sizes of 150 Mpc, which are an order of
magnitude smaller than the observed GRB ring diameter. Evidence in support of
the shell interpretation requires that temporal information of the transient GRBs be
included in the analysis.
This ring-shaped feature is large enough to contradict the cosmological principle.
The physical mechanism responsible for causing it is unknown.
Key words: Large-scale structure of Universe, cosmology: observations, gamma-ray
burst: general
1
INTRODUCTION
Quasars are well-suited for mapping out the large-scale
distribution of matter in the Universe, due to their very
high luminosities and preferentially large redshifts. Quasars
are associated by groups and poor clusters of galaxies
(Hein¨
am¨
aki et al. 2005; Lietzen et al. 2009) and can be observed even when the underlying galaxies are faint and difficult to detect. When quasars cluster, they identify considerable amounts of underlying matter, such that quasar
clusters have been used to detect matter clustered on very
large scales. Some of this matter is clustered on scales equal
to or exceeding that of the Sloan Great Wall (Gott et al.
2005).
A number of large quasar groups (LQG) have been iden-
⋆
E-mail, [email protected]
c RAS
tified in recent years; each one mapping out large amounts
of much fainter matter. After Webster (1982) found a group
of four quasars at z = 0.37 with a size of about 100
Mpc, having a low probability of being a chance alignment,
Komberg, Kravtsov & Lukash (1994) identified strong clustering in the quasar distribution at scales less than 20 h−1
Mpc, and defined LQGs using a well-known cluster analysis technique. Subsequently, Komberg, Kravtsov & Lukash
(1996) identified additional LQGs, and Komberg & Lukash
(1998) reported a new finding of eleven LQGs based on systematic cluster analysis. The sizes of these clusters ranged
from 70 to 160 h−1 Mpc. Newman et al. (1998a,b) later
discovered a 150 h−1 Mpc group of 13 quasars at median
redshift z ∼
= 1.51. Williger et al. (2002) mapped 18 quasars
spanning ≈ 5◦ × 2.5◦ on the sky, with a quasar spatial overdensity 6−10 times greater than the mean. Haberzettl et al.
(2009) investigated two sheet-like structures of galaxies at
Galaxy And Mass Assembly (GAMA): A study of energy, mass, and
structure (1kpc-1Mpc) at z < 0.3
Simon P. Driver,1,2 (and the GAMA team)
1 International
Centre for Radio Astronomy Research (ICRAR), School of
Physics, University of Western Australia, Crawley, Perth, WA 6009, Australia;
Simon.Driver@ uwa.edu.au
2 SUPA,
School of Physics and Astronomy, University of St Andrews, North
Haugh, St Andrews, Fife, KY16 9SS, UK, spd3@ st-and.ac.uk
Abstract.
The GAMA survey has now completed its spectroscopic campaign of
over 250,000 galaxies (r < 19.8mag), and will shortly complete the assimilation of the
complementary panchromatic imaging data from GALEX, VST, VISTA, WISE, and
Herschel. In the coming years the GAMA fields will be observed by the Australian
Square Kilometer Array Pathfinder allowing a complete study of the stellar, dust, and
gas mass constituents of galaxies within the low-z Universe (z < 0.3). The science
directive is to study the distribution of mass, energy, and structure on kpc-Mpc scales
over a 3billion year timeline. This is being pursued both as an empirical study in its
own right, as well as providing a benchmark resource against which the outputs from
numerical simulations can be compared. GAMA has three particularly compelling aspects which set it apart: completeness, selection, and panchromatic coverage. The very
high redshift completeness (∼ 98%) allows for extremely complete and robust pair and
group catalogues; the simple selection (r < 19.8mag) minimises the selection bias and
simplifies its management; and the panchromatic coverage, 0.2µm - 1m, enables studies
of the complete energy distributions for individual galaxies, well defined sub-samples,
and population assembles (either directly or via stacking techniques). For further details
and data releases see: http://www.gama-survey.org
1. Introduction
Extra-galactic studies, in and around the 21st century, can arguably be broken down
into four distinct categories: Focused experiments (e.g., WiggleZ, BOSS, DES, Euclid);
high-fidelity studies of well selected sub-samples (e.g., S4 G, ATLAS3D, MANGA etc);
frontier studies (e.g., HDF, UDF, Frontier’s fields); and open-ended legacy studies (e.g.,
2MASS, SDSS, COSMOS, GEMS, CANDLES). These distinct approaches are all important and highly complementary. The Galaxy And Mass Assembly survey (GAMA;
Driver et al. 2011), very much fits into the latter category, by providing a broad legacy
resource to the community, with a key focus on being comprehensive and complete.
GAMA, like its predecessors the SDSS and 2MASS, is now forming the basis for highfidelity follow-on studies (e.g., SAMI/IFU, ASKAP/DINGO, Euclid Legacy Science),
and even frontier studies (e.g., HST lens sample, JWST usage of GAMA groups as
probes to z > 10). Internally the GAMA team now consists of over 100 scientists
studying the distribution and evolution of mass, energy, and structure with data also
flowing through to external teams fueling collaborative projects.
1
Confined Flares in Solar Active Region 12192 from 2014 October
18 to 29
Huadong Chen1 , Jun Zhang1 , Suli Ma2 , Shuhong Yang1 , Leping Li1 , Xin Huang1 , Junmin
Xiao1
[email protected]
ABSTRACT
Using the observations from the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) aboard the
Solar Dynamics Observatory (SDO), we investigate six X-class and twentynine M-class flares occurring in solar active region (AR) 12192 from October
18 to 29. Among them, thirty (including six X- and twenty-four M-class)
flares originated from the AR core and the other five M-flares appeared at
the AR periphery. Four of the X-flares exhibited similar flaring structures,
indicating they were homologous flares with analogous triggering mechanism.
The possible scenario is: photospheric motions of emerged magnetic fluxes
lead to shearing of the associated coronal magnetic field, which then yields a
tether-cutting favorable configuration. Among the five periphery M-flares,
four were associated with jet activities. The HMI vertical magnetic field data
show that the photospheric fluxes of opposite magnetic polarities emerged,
converged and canceled with each other at the footpoints of the jets before
the flares. Only one M-flare from the AR periphery was followed by a coronal
mass ejection (CME). From October 20 to 26, the mean decay index of the
horizontal background field within the height range of 40–105 Mm is below
the typical threshold for torus instability onset. This suggests that a strong
confinement from the overlying magnetic field might be responsible for the poor
CME production of AR 12192.
Subject headings: Sun: activity — Sun: coronal mass ejections (CMEs) — Sun:
flares — Sun: UV radiation
1
Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences,
Beijing 100012, China
2
College of Science, China University of Petroleum, Qingdao 266580, China
Mon. Not. R. Astron. Soc. 000, 1–6 (2015)
Printed 3 July 2015
arXiv:1507.00643v1 [astro-ph.HE] 2 Jul 2015
On the variable timing behavior of PSR B0540−69 and
PSR J1846−0258
F. F. Kou, Z. W. Ou & H. Tong⋆
Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi, Xinjiang 830011, China
2015.7 v1
ABSTRACT
The pulsar wind model is applied to explain the variable timing behavior of PSR
B0540−69 and PSR J1846−0258. For PSR B0540−69, a 36% relative increase in the
spin down rate was reported recently. Similarly, a net decrease in the spin frequency
∆ν ≈ −10−4 Hz after a large glitch and a lower braking index were detected for PSR
J1846−0258. In the pulsar wind model, braking indices of these two pulsar which are
all larger than 1 but smaller than 3 can be well explained. The particle density reflects
the magnetospheric activity in real-time and may be responsible for the changing
spin down behavior. A different state of particle density (κ0 ± ∆κ) will result in
increase (or decrease) in the spin down rate. Corresponding to the variable timing
behavior of PSR B0540−69 and PSR J1846−0258, the relative increase in the particle
density are respectively 88% and 44% in the vacuum gap model. A changing particle
density (κ(t)) will lead to a varying braking index. The changing particle density is
κ˙ = 1.68 × 10−9 s−1 for PSR J1846−0258 corresponding to its lower braking index
2.19 ± 0.03.
Key words:
pulsars: general – pulsars: individual (PSR B0540−69; PSR
J1846−0258) – stars: neutron – wind
1
INTRODUCTION
PSR B0540−69, known as the “Crab Twin”, is a young radio pulsar with a characteristic magnetic field about 1013 G
at the magnetic poles1 . It was discovered with the Einstein Observatory (Seward, Harnden & Helfand 1984) and
had been long-term monitored by the RXTE satellite etc.
Only two glitches with relative small changes in spin down
parameters were reported (Zhang et al. 2001; Cusumano,
Massaro & Mineo 2003; Livingstone, Kaspi& Gavriil 2005;
Ferdman, Archibald & Kaspi 2015). Recently, a persistent
and unprecedented increase in the spin down rate of PSR
B0540−69 was reported: the relative increase in the spindown rate is 36% which is orders magnitude larger than the
changes induced by glitches (Marshall, Guillemot & Harding
2015). Coincidentally, a net decrease in the spin frequency
(∆ν ≈ −104 Hz) after the large glitch had been observed
for PSR J1846−0258 (Livingstone, Kaspi, & Gavriil 2010).
Besides, just like the Crab pulsar, a lower braking index
n = 2.19±0.03 of PSR J1846−0258 was detected later which
obviously deviates from the pre-outburst value 2.65 ± 0.01
(Livingstone et al. 2006, 2011; Archibald et al. 2015b). These
⋆
Corresponding author: [email protected]
Assuming all the rotational energy is consumed
pby magneto19
dipole radiation in vacuum, B(pole) = 6.4 × 10
P P˙ G
1
two sources are just two examples of the variable timing behavior of pulsars. The physics behind the variable timing
behavior is still unknown.
The spin down behavior of pulsars can be described by
the power law:
ν˙ = −Cν n ,
(1)
where ν and ν˙ are respectively the spin down frequency and
frequency derivative, C is usually taken as a constant and n
is the braking index. The braking index is defined accordingly:
n=
ν ν¨
,
ν˙ 2
(2)
where ν¨ is the second derivative of spin frequency. The
braking index reflects the pulsar braking mechanism (Tong
2015). In the magneto-dipole braking model, a pulsar ro2 2
µ
ν 3 sin2 α. Where µ =
tates uniformly in vacuum ν˙ = − 8π
3Ic3
3
1/2BR is the magnetic dipole moment and I = 1045 g cm2
is the moment of inertia, c is the speed of light, and α is
the angle between the rotational axis and the magnetic axis
(i.e. the inclination angle). The braking index is three in
the magnetic dipole braking model. It is not consistent with
the braking index observations of pulsars (Lyne et al. 2015)
Furthermore, the fundamental assumption of the magnetic
dipole braking model (vacuum condition) does not exist
Theoretical Estimate of the
Sensitivity of the CUORE Detector
to Solar Axions
Dawei. Li,a,1 R.J. Creswick,a F.T. Avignone III,a and Yuanxu.
Wangb
a Department
b School
of Physics and Astronomy, University of South Carolina, Columbia, SC, USA
of Physics and Electronics, Henan University, Kaifeng, Henan, China
Abstract. In this paper we calculate the potential sensitivity of the CUORE detector to
axions produced in the Sun through the Primakoff process and detected by coherent Bragg
conversion by the inverse Primakoff process. The conversion rate is calculated using density
functional theory for the electron density and realistic expectations for the energy resolution
and background of CUORE. Monte Carlo calculations for 5 y×741 kg=3705 kg y of exposure
are analyzed using time correlation of individual events with the theoretical time-dependent
counting rate and lead to an expected limit on the axion-photon coupling gaγγ < 3.83 ×
10−10 GeV −1 for axion masses less than several eV.
1
Corresponding author.
c
ESO
2015
Astronomy & Astrophysics manuscript no. gx304
July 3, 2015
Luminosity-dependent spectral and timing properties of the
accreting pulsar GX 304−1 measured with INTEGRAL
C. Malacaria, D. Klochkov, A. Santangelo, and R. Staubert
Institut für Astronomie und Astrophysik, Sand 1, 72076 Tübingen, Germany
July 3, 2015
ABSTRACT
Context. Be/X-ray binaries show outbursts with peak luminosities up to a few times 1037 erg/s, during which they can be observed and
studied in detail. Most (if not all) Be/X-ray binaries harbour accreting pulsars, whose X-ray spectra in many cases contain cyclotron
resonant scattering features related to the magnetic field of the sources. Spectral variations as a function of luminosity and of the
rotational phase of the neutron star are observed in many accreting pulsars.
Aims. We explore X-ray spectral and timing properties of the Be/X-ray binary GX 304-1 during an outburst episode. Specifically,
we investigate the behavior of the cyclotron resonant scattering feature, the continuum spectral parameters, the pulse period, and
the energy- and luminosity-resolved pulse profiles. We combine the luminosity-resolved spectral and timing analysis to probe the
accretion geometry and the beaming patterns of the rotating neutron star.
Methods. We analyze the INTEGRAL data from the two JEM-X modules, ISGRI and SPI, covering the January-February 2012
outburst, divided in six observations. We obtain pulse profiles in two energy bands, phase-averaged and phase-resolved spectra for
each observation.
Results. We confirm the positive luminosity-dependence of the cyclotron line energy in GX 304-1, and report a dependence of the
photon index on luminosity. Using a pulse-phase connection technique, we find a pulse period solution valid for the entire outburst.
Our pulse-phase resolved analysis shows, that the centroid energy of the cyclotron line is varying only slightly with pulse phase, while
other spectral parameters show more pronounced variations. Our results are consistent with a scenario in which, as the pulsar rotates,
we are exploring only a small portion of its beam pattern.
Key words. X-rays: binaries – stars: neutron – accretion, accretion disks – pulsars: individual: GX 304-1
1. Introduction
GX 304-1 is a Be/X-ray binary (BeXRB) system discovered as
an X-ray source in 1967 during a balloon observation (Lewin
et al. 1968a,b). Subsequently, the source was established to be
an X-ray pulsar with a pulse period of ∼ 272 s (McClintock
et al. 1977). A study of the recurrent outburst activity revealed
a ∼ 132.5 d periodicity, likely due to the system’s orbital period
(Priedhorsky & Terrell 1983). The optical counterpart of the binary is a B2 Vne star, whose distance has been measured to be
2.4 ± 0.5 kpc (Parkes et al. 1980). Since 1980, the source entered
an X-ray off-state (Pietsch et al. 1986), showing no detectable
emission for 28 years. The quiescence was interrupted in June
2008, when INTEGRAL detected hard X-ray emission from the
source (Manousakis et al. 2008). Since then, GX 304-1 lighted
up repeatedly, becoming a periodically outbursting X-ray source.
The period of the outbursts after 2009 is roughly the same as before 1980, i.e., ∼132.5 d. The peak luminosities are .1037 erg/s
in the 5 − 100 keV energy band. The origin of the X-ray emission is believed to be accretion of matter from the circumstellar
equatorial disk around the optical companion onto a magnetized
neutron star. The strong magnetic field of the accretor (∼1012 G)
channels the captured matter towards its magnetic poles where
X-ray emission originates in an accretion structure.
A Cyclotron Resonant Scattering feature (CRSF), or cyclotron line, has been detected in the spectrum of GX 304-1 with
a centroid energy of ∼ 52 keV (Yamamoto et al. 2011). CRSFs
are important features in the spectra of accreting pulsars. In a
strong magnetic field, electron energies corresponding to their
motion perpendicular to the magnetic field lines are quantized
in Landau levels, causing resonant scattering of impinging photons. The first such line ever was detected in data from a balloon
observation of Her X-1 (Trümper et al. 1978). Nowadays, they
have turned out to be rather common in accreting X-ray pulsars, with ∼ 20 objects being confirmed cyclotron line sources,
with several objects showing multiple lines (up to four harmonics in 4U 0115+63, Santangelo et al. 1999). Reviews are
given by e.g. Coburn et al. (2002); Staubert (2003); Heindl et al.
(2004); Terada et al. (2007); Wilms (2012); Caballero & Wilms
(2012). The energy of the fundamental line Ecyc is directly proportional to the magnetic field strength at the emission site,
Ecyc ∼ 11.6 × B12 (1 + zg ) keV, where B12 is the magnetic field in
units of 1012 G, and zg is the gravitational redshift.
More recent observations have shown that the cyclotron line
energy in GX 304-1 is positively correlated with the observed
luminosity (Klochkov et al. 2012). Such a positive correlation
was first observed in Her X-1 by Staubert et al. (2007) and is
now observed also for GX 304-1 , Vela X-1 (Fürst et al. 2014)
and recently also for A 0535+26 (Sartore et al. 2015).
The opposite correlation, a negative dependence between
the cyclotron line energy and the luminosity, was actually detected earlier in high luminosity transient sources (4U 0115+63,
Cep X-4, and V 0332+53, Mihara et al. 1998). During the
2004/2005 outburst of V 0332+53, a clear anti-correlation of
Article number, page 1 of 12
c
ESO
2015
Astronomy & Astrophysics manuscript no. SelfGen
July 3, 2015
Non-linear cosmic ray Galactic transport
in the light of AMS-02 and Voyager data
(Research Note)
R. Aloisio,1, 2 P. Blasi2, 1 and P. D. Serpico3
1
2
3
Gran Sasso Science Institute (INFN), Viale F. Crispi 7, 67100 L’Aquila, Italy
INAF/Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5 50125 Firenze, Italy
LAPTh, Univ. Savoie Mont Blanc, CNRS, B.P.110, Annecy-le-Vieux F-74941, France
Received; accepted
Preprint numbers: LAPTH-036/15
ABSTRACT
Context. Features in the spectra of primary cosmic rays (CRs) provide invaluable information on the propagation of these particles in
the Galaxy. In the rigidity region around a few hundred GV, such features have been measured in the proton and helium spectra by the
PAMELA experiment and later confirmed with a higher significance by AMS-02. We investigate the implications of these datasets
for the scenario in which CRs propagate under the action of self-generated waves.
Aims. We show that the recent data on the spectrum of protons and helium nuclei as collected with AMS-02 and Voyager are in very
good agreement with the predictions of a model in which the transport of Galactic CRs is regulated by self-generated waves. We
also study the implications of the scenario for the boron-to-carbon ratio: although a good overall agreement is found, at high energy
we find marginal support for a (quasi) energy independent contribution to the grammage, that we argue may come from the sources
themselves.
Methods. The transport equation for both primary and secondary nuclei is solved together with an equation for the evolution of the
self-generated waves and a background of pre-existing waves. The solution of this system of non-linear equations is found with an
iterative method elaborated by the same authors in previous work on this topic.
Results. A break in the spectra of all nuclei is found at rigidity of a few hundred GV, as a result of a transition from self-generated
waves to pre-existing waves with a Kolmogorov power spectrum. Neither the slope of the diffusion coefficient, nor its normalisation
are free parameters. Moreover, at rigidities below a few GV, CRs are predicted to be advected with the self-generated waves at the
local Alfvén speed. This effect, predicted in our previous work, provides an excellent fit to the Voyager data on the proton and helium
spectra at low energies, providing additional support to the model.
1. Introduction
The transport of Galactic cosmic rays (CRs) is likely to be very
complex: the structure of the large scale magnetic field is complicated and very poorly known, and the structures on small scales
(resonant with the CR particles) are basically unknown, although
the fact that the diffusion paradigm seems to work can be considered as an indirect evidence for the existence of such small
scale turbulence. The origin of the power on small scales is also
unknown, but one contribution that seems to be hardly avoidable is that due to the self-generation of perturbations due to the
CR current, proportional to the gradient of CRs, which in turn
is due to the existence of the same scattering centres, responsible for diffusion. This simple description is sufficient to emphasise the non-linear nature of this process, which is qualitatively
similar to what happens at supernova shocks, thought to be the
main sources of Galactic CRs (see the recent review by Blasi
(2013)). In addition to the self-generated waves, turbulence at
larger spatial scales is generically expected and becomes important for scattering CRs of higher energies.
This scenario has been analysed in detail in (Blasi et al.
2012; Aloisio 2013), where the main implications were discussed: Blasi et al. (2012) calculated the spectrum of protons
under the action of both the self-generated and pre-existing turbulence, and compared the results with the PAMELA data available at the time (Adriani 2011), where the first direct detection of
a spectral break in proton and helium fluxes at few hundred GV
was claimed. The first release of the data collected by AMS-02
(Haino 2013; Choutko 2013) did not confirm the existence of
these spectral features and brought the investigation on this topic
to an almost complete standstill, waiting for the resolution of
the observational conundrum. Recently the AMS collaboration
published the final analysis of the data on the proton spectrum
(Aguilar et al. 2015), where a change of slope at few hundred
GV is evident. At the present time, only preliminary results on
the spectrum of helium and carbon nuclei are available (AMS-02
2015), but a similar break is visible in such data as well. Moreover, preliminary data on the B/C ratio have also been presented:
the small statistical error bars up to high energies allow us to
use this tool as a powerful indicator of the propagation of CRs
through the Galaxy.
In addition to the AMS-02 data, the results of another invaluable experimental effort became available in the last few years:
the Voyager spacecraft, launched in 1977, reached the termination shock and is now believed to be moving in the interstellar medium, unaffected by the solar wind (Stone et al. 2013).
Solar Physics
DOI: 10.1007/•••••-•••-•••-••••-•
Quantifying the Difference Between the Flux-Tube
Expansion Factor at the Source Surface and at the
Alfv´
en Surface Using A Global MHD Model for the
Solar Wind
O. Cohen1 ·
c Springer ••••
Abstract
The potential field approximation has been providing a fast, and computationally
inexpensive estimation for the solar corona’s global magnetic field geometry for
several decades. In contrast, more physics-based global magnetohydrodynamic
(MHD) models have been used for a similar purpose, while being much more
computationally expensive. Here, we investigate the difference in the field geometry between a global MHD model and the potential field source surface model
(PFSSM) by tracing individual magnetic field lines in the MHD model from
the Alfvén surface (AS), through the source surface (SS), all the way to the
field line footpoint, and then back to the source surface in the PFSSM. We also
compare the flux-tube expansion at two points at the SS and the AS along the
same radial line. We study the effect of solar cycle variations, the order of the
potential field harmonic expansion, and different magnetogram sources. We find
that the flux-tube expansion factor is consistently smaller at the AS than at the
SS for solar minimum and the fast solar wind, but it is consistently larger for
solar maximum and the slow solar wind. We use the Wang–Sheeley–Arge (WSA)
model to calculate the associated wind speed for each field line, and propagate
these solar-wind speeds to 1 AU. We find a more than five hours deviation in
the arrival time between the two models for 20 % of the field lines in the solar
minimum case, and for 40 % of the field lines in the solar maximum case.
Keywords: Magnetic fields, Models — Solar Wind, Theory — Velocity Fields,
Solar Wind
1. Introduction
The magnetic field above the solar photosphere and in the solar corona is
weak. Therefore, it is hard to obtain observationally the three-dimensional topol1 Harvard-Smithsonian Center for Astrophysics,
60 Garden St. Cambridge, MA 02138,
USA email: [email protected]
SOLA: ms.tex; 3 July 2015; 0:37; p. 1
Heliosphere for a wide range of interstellar magnetic field
strengths as a source of energetic neutral atoms
A. Czechowski1 and J. Grygorczuk2
Space Research Centre, Polish Academy of Sciences, Bartycka 18A, 00-716 Warsaw, Poland
and
D. J. McComas3
Southwest Research Institute, San Antonio, TX 78228 USA
and
Dept. of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX 78249, U.S.A.
ABSTRACT
Observations of the energetic neutral atoms (ENAs) of heliospheric origin by IBEX differ from
expectations based on heliospheric models. It was proposed that the structure of the heliosphere
may be similar to the ”two-stream” model derived in 1961 by Parker for the case of strong
interstellar magnetic field.
Using MHD simulations, we examine possible structure of the heliosphere for a wide range of
interstellar magnetic field strengths, with different choices of interstellar medium and solar wind
parameters. For the model heliospheres, we calculate the fluxes of ENAs created in the inner
heliosheath, and compare with IBEX observations.
We find that the plasma flow in the model heliospheres for strong interstellar field (∼20 µG)
has a ”two-stream” structure, which remains visible down to ∼5 µG. The obtained ENA flux
distribution show the features similar to the ”split tail” effect observed by IBEX. In our model,
the main cause of this effect is the two component (fast and slow) solar wind structure.
Subject headings: Sun: heliosphere — Sun: solar wind — ISM: magnetic fields — magnetohydrodynamics
1.
sphere in the case of the Sun) were first introduced
in the classic work by Parker (1961). As shown
by Parker, in the case of a star moving through
unmagnetized interstellar plasma, the stellar wind
flow, after passing the termination shock, turns
ultimately in the direction opposite to the motion
of the star, forming the ”tail” (heliotail). This
structure was indeed obtained in all models of the
heliosphere based on numerical solutions of the gas
dynamical or MHD equations.
Recently, another class of these models was
included in the discussion. As again shown by
Parker (1961), in the case of a star at rest with respect to the interstellar medium with strong magnetic field, the stellar wind may form, instead of
a single astrotail, two oppositely directed streams
Introduction
Energetic neutral atoms (ENAs) created in the
distant heliosphere by energetic ion neutralization
provide a means to remotely observe the distant
regions of the heliosphere. Theoretical models of
the large scale structure of the heliosphere are important for understanding and interpreting these
observations.
The global models of the stellar wind interaction with the interstellar medium (ISM), leading
to the formation of the astrospheres (the helio1 e-mail:
[email protected]
[email protected]
3 e-mail: [email protected]
2 e-mail:
1
c
ESO
2015
Astronomy & Astrophysics manuscript no. new
July 3, 2015
Relationship between the column density distribution and
evolutionary class of molecular clouds as viewed by ATLASGAL
Abreu-Vicente, J.1⋆ , Kainulainen, J.1 , Stutz, A.1 , Henning, Th.1 , Beuther, H.1
Max-Planck-Institut für Astronomie (MPIA), Königstuhl 17, 69117, Heidelberg, Germany
July 3, 2015
ABSTRACT
We present the first study of the relationship between the column density distribution of molecular clouds within nearby Galactic
spiral arms and their evolutionary status as measured from their stellar content. We analyze a sample of 195 molecular clouds located
at distances below 5.5 kpc, identified from the ATLASGAL 870 µm data. We define three evolutionary classes within this sample:
starless clumps, star-forming clouds with associated young stellar objects, and clouds associated with H ii regions. We find that the
N(H2 ) probability density functions (N-PDFs) of these three classes of objects are clearly different: the N-PDFs of starless clumps are
narrowest and close to log-normal in shape, while star-forming clouds and H ii regions exhibit a power-law shape over a wide range
of column densities and log-normal-like components only at low column densities. We use the N-PDFs to estimate the evolutionary
time-scales of the three classes of objects based on a simple analytic model from literature. Finally, we show that the integral of the
N-PDFs, the dense gas mass fraction, depends on the total mass of the regions as measured by ATLASGAL: more massive clouds
contain greater relative amounts of dense gas across all evolutionary classes.
Key words. ISM: clouds – dust – extinction – ISM: structure – stars: formation – infrared: ISM
1. Introduction
Molecular clouds (MCs) are the densest regions of the interstellar medium and the birth sites of stars. Nevertheless, despite this
important role in star formation, key aspects of MC evolution
remain unclear: What are the key parameters in determining the
star-forming activity of MCs? How do these parameters change
with MC evolution? The column density distribution of MCs
has been found to be sensitive to the relevant physical processes
(Hennebelle & Falgarone 2012). The study of the density structure of clouds that are at different evolutionary stages can therefore help to understand which physical processes are dominating
the cloud structure at those stages.
Column density probability density functions (N-PDFs) are
useful tools for inferring the role of different physical processes in shaping the structure of molecular clouds. Observations have shown that non-star-forming molecular clouds show
bottom-heavy1 N-PDFs, while the star-forming molecular clouds
show top-heavy2 N-PDFs (Kainulainen et al. 2009, 2011b, 2014;
Kainulainen & Tan 2013; Schneider et al. 2013). It is generally
accepted that the top-heavy N-PDFs are well described by a
power-law function in their high-column density regimes. The
description of the shapes of the low-column density regimes of
both kinds of N-PDFs is still a matter of debate. The papers cited
above describe the low-column density regimes as log-normal
functions. In contrast, Alves et al. (2014) and Lombardi et al.
(2015) argue that a power-law function fits the observed N-PDFs
Send
offprint
requests
to:
J.
Abreu-Vicente,
e-mail:
[email protected]
⋆
Member of the International Max Planck Research School (IMPRS)
at the University of Heidelberg
1
Most of their mass is in low-column density material.
2
They have a significant amount of mass enclosed in high-column
density regions.
throughout their range. The origin of these differences is currently unclear.
Simulations predict that turbulence-dominated gas develops a log-normal N-PDF (Federrath & Klessen 2013); such
a form is predicted for the volume density PDF (hereafter
ρ-PDF) of isothermal, supersonic turbulent, and non-selfgravitating gas (Vazquez-Semadeni 1994; Padoan et al. 1997;
Scalo et al. 1998; Ostriker et al. 2001; Padoan & Nordlund
2011; Ballesteros-Paredes et al. 2011; Federrath & Klessen
2013). Log-normal ρ-PDFs can, however, result also from
processes other than supersonic turbulence such as gravity opposed only by thermal-pressure forces or gravitationally-driven
ambipolar diffusion (Tassis et al. 2010).
The log-normal N-PDF is defined as:
!
−(s − µ)2
1
,
p(s; µ, σ s ) =
√ exp
2σ2s
σ s 2π
(1)
where s = ln (AV /AV ) is the mean-normalized visual extinction (tracer of column density, see Section 2.3), and µ and
σ s are respectively the mean and standard deviation of the
distribution. The log-normal component that is used to describe low column densities has typically the width of σ s =
0.3 − 0.4 (Kainulainen et al. 2009). It has been suggested that
the determination of the width can be affected by issues such
as unrelated dust emission along the line of sight to the
cloud (Schneider et al. 2015). Practically all star-forming clouds
in the Solar neighborhood show an excess to this component at
higher column densities, following a power-law, or a wider lognormal function (Kainulainen et al. 2009; Kainulainen & Tan
2013; Schneider et al. 2013), especially reflecting their ongoing
star formation activity (Kainulainen et al. 2014; Sadavoy et al.
2014; Stutz & Kainulainen 2015). Such behavior is suggested
Detecting gravitational-wave transients at five sigma:
a hierarchical approach
Eric Thrane1, a and Michael Coughlin2
arXiv:1507.00537v1 [astro-ph.IM] 2 Jul 2015
1
School of Physics and Astronomy, Monash University, Clayton, Victoria 3800, Australia
2
Department of Physics, Harvard University, Cambridge, MA 02138, USA
As second-generation gravitational-wave detectors prepare to analyze data at unprecedented sensitivity, there is great interest in searches for unmodeled transients, commonly called bursts. Significant effort has yielded a variety of techniques to identify and characterize such transient signals,
and many of these methods have been applied to produce astrophysical results using data from
first-generation detectors. However, the computational cost of background estimation remains a
challenging problem; it is difficult to claim a 5σ detection with reasonable computational resources
without paying for efficiency with reduced sensitivity. We demonstrate a hierarchical approach to
gravitational-wave transient detection, focusing on long-lived signals, which can be used to detect
transients with significance in excess of 5σ using modest computational resources. In particular, we
show how previously developed seedless clustering techniques can be applied to large datasets to
identify high-significance candidates without having to trade sensitivity for speed.
Introduction. With second-generation gravitationalwave (GW) detectors coming online later this year, the
first direct detection of GWs may be near. In order to
establish the significance of a detection, it is common to
report a false alarm probability (FAP), which quantifies
the probability that a noise fluctuation could produce
an event at least as loud as the observed candidate (as
measured by some detection statistic). In some subfields,
e.g., particle physics,“5σ significance,” corresponding to
FAP ≈ 5.7 × 10−7 , is used as a detection threshold.
In order to estimate the FAP of a GW candidate, it is
common to perform time-shifts in which the GW strain
time series from one detector is shifted with respect to the
series from a second detector by an amount greater than
both the travel time between the detectors and the coherence time of the signals being targeted. Time-shifting
preserves non-Gaussian and non-stationary features that
characterize the zero-lag (no time-shift) noise, while simultaneously eliminating true GW signals. By performing N time-shifts, it is possible to generate a distribution
of the detection statistic, which can be used to estimate
FAP to a level of ≥ 1/N . The 5σ threshold corresponds
to N ≈ 1.7 × 106 . In many cases it is computationally
impractical to carry out this many time-shifts, though, it
has been accomplished in the “detection” of a LIGO blind
injection with a matched filter search [1]. Despite the
pervasive use of time-shifts, there are limitations [2, 3].
For many transient GW searches, the significant computing costs incurred by background estimation arise
from a desire to use a coherent detection statistic. Coherent algorithms utilize the complex-valued cross-power
obtained by cross-correlating strain data from ≥2 detectors instead of or in addition to the incoherent autopower observed in each detector separately; see, e.g., [4–
7]. The extra phase information helps differentiate sig-
a Electronic
nal from background, improving the sensitivity of the
search. However, the cost of background estimation for
coherent searches is relatively large compared to a comparable incoherent search because the detection statistic
must be recalculated for each time-shift, after the fresh
application of a clustering algorithm. Some algorithms
use single-detector auto-power exclusively, which allows
for much more rapid background estimation [8, 9].
In this Letter, we describe a hierarchical approach to
background estimation in the context of a search for longlived, unmodeled GW transients using seedless clustering [10, 11]. First, we identify “events” using a computationally intensive, but incoherent, single-detector statistic. Second, we calculate a computationally fast, coherent detection statistic for each event identified with the
single-detector statistic. The second, coherent detection
statistic is used to evaluate significance. By splitting the
calculation into an incoherent stage and a coherent stage,
it is possible to carry out computationally intensive calculations just once, allowing rapid background estimation
without sacrificing the sensitivity gained by the use of
coherence.
We demonstrate this technique by estimating the
background—past the 5σ level—for two weeks of simulated Monte Carlo data and two weeks of Initial
LIGO noise, recolored to resemble data from Advanced
LIGO [12]. We calculate the sensitivity of this mock
search for several toy model waveforms and find that it
is not adversely affected by the incoherent stage.
The remainder of this Letter is organized as follows.
We review the basics of transient identification with seedless clustering and describe the details of the new hierarchical detection statistic, we describe a mock analysis
carried out on two weeks of Monte Carlo data and two
weeks of recolored Initial LIGO noise, and we present results demonstrating the ability to estimate background
at the 5σ level.
Method. In previous work, we have described seedless clustering [10, 11, 13–15], a technique in which GW
July 3, 2015
0:23
WSPC Proceedings - 9.75in x 6.5in
proceedings
1
Super Massive Black Holes and the Origin of High-Velocity Stars
Roberto Capuzzo-Dolcetta∗ and Giacomo Fragione∗∗
Dep. of Physics, Sapienza, Univ. of Roma
P.le A. Moro 2, Roma, Italy
∗ E-mail: [email protected]
∗∗ E-mail: [email protected]
The origin of high velocity stars observed in the halo of our Galaxy is still unclear. In
this work we test the hypothesis, raised by results of recent high precision N -body simulations, of strong acceleration of stars belonging to a massive globular cluster orbitally
decayed in the central region of the host galaxy where it suffers of a close interaction
with a super massive black hole, which, for these test cases, we assumed 108 M⊙ in mass.
Keywords: galaxies: haloes, nuclei, super massive black holes, clusters.
1. Introduction
Hypervelocity stars (HVS) are stars escaping the host galaxy. Hills 6 was the first to
predict theoretically their existence as a consequence of interactions with a massive
Black Hole (BH) in the Galactic Centre 6 , while Brown et al. serendipitously discovered the first HVS in the outer stellar halo of the Galaxy, a B-type star moving over
twice the Galactic escape velocity 2 . The most recent HVS Survey is the Multiple
Mirror Telescope Survey, which revealed 21 HVSs at distances between 50 and 120
kpc 3 .
Hills’ mechanism involves the tidal breakup of a binary passing close to a massive
BH, which could lead also to a population of stars orbiting in the inner regions of the
Galaxy around the central BH, the so-called S stars 9 . Since the Hills’ prediction,
many other mechanisms have been proposed to explain the production of HVSs,
which involve different astrophysical frameworks and phenomena 10,11 . The study
of the characteristics of these stars would help to infer information on both the
small and large scales of the Galaxy, i.e. the region near massive BHs as well the
shape of the Galaxy and Dark Matter gravitational potential 5 .
The aim of the present work is to investigate another mechanism of production
of HVS, which involve a Globular Cluster (GC) that during its orbit has the chance
to pass close to a super massive black hole (SMBH) in the center of its host galaxy.
2. Close Globular Cluster-Super Massive Black Hole Interactions
From direct N -body simulations of a GC passing close to an SMBH 1 , there is
evidence that some GC stars are ejected in sort of jets. Therefore, in order to
understand the underlying physical mechanism leading to such ejections, we performed 3-body scattering experiments involving an SMBH, a GC and a star. In our
simulations the BH is initially set in the origin of the reference frame, while the GC
(considered as a point mass) follows an elliptical orbit around it within the SMBH
influence radius. This assumption is justified by that the GC has had the time
page 1
Solar and Heliospheric Physics with the Square
Kilometre Array
Valery M. Nakariakov1, Mario M. Bisi2 , Philippa K. Browning3, Dalmiro Maia4 ,
Eduard P. Kontar5 , Divya Oberoi6 , Peter T. Gallagher7 , Iver H. Cairns8 , Heather
Ratcliffe1
1 Centre for Fusion, Space and Astrophysics, Physics Department, University of Warwick,
Coventry CV4 7AL, UK; 2 RAL Space, Science & Technology Facilities Council – Rutherford
Appleton Laboratory, Harwell Oxford, Oxfordshire, OX11 0QX, England, UK; 3 Jodrell Bank
Centre for Astrophysics, University of Manchester, Manchester, M13 9PL, UK; 4 CICGE,
Observatorio Astronomico Professor Manuel de Barros, Faculdade de Ciencias da Universidade
do Porto, Vila Nova de Gaia, Portugal; 5 School of Physics and Astronomy, University of
Glasgow, Glasgow, G12 8QQ, UK; 6 National Centre for Radio Astrophysics, Tata Institute of
Fundamental Research, India; 7 School of Physics, Trinity College Dublin, 2, Dublin, Ireland;
8 School of Physics, University of Sydney, Sydney, NSW 2006, Australia.
E-mail: V.Nakariakov at warwick.ac.uk; Mario.Bisi at stfc.ac.uk
The fields of solar radiophysics and solar system radio physics, or radio heliophysics, will benefit
immensely from an instrument with the capabilities projected for SKA. Potential applications include interplanetary scintillation (IPS), radio-burst tracking, and solar spectral radio imaging with
a superior sensitivity. These will provide breakthrough new insights and results in topics of fundamental importance, such as the physics of impulsive energy releases, magnetohydrodynamic
oscillations and turbulence, the dynamics of post-eruptive processes, energetic particle acceleration, the structure of the solar wind and the development and evolution of solar wind transients at
distances up to and beyond the orbit of the Earth. The combination of the high spectral, time and
spatial resolution and the unprecedented sensitivity of the SKA will radically advance our understanding of basic physical processes operating in solar and heliospheric plasmas and provide a
solid foundation for the forecasting of space weather events.
Advancing Astrophysics with the Square Kilometre Array
June 8-13, 2014
Giardini Naxos, Sicily, Italy
© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
http://pos.sissa.it/
Solar and Heliospheric Physics with SKA
1. Introduction
The Sun is the brightest radio object in the Universe visible from the Earth. In powerful flares,
the radio flux density may exceed 109 Jy. The wide variety of mechanisms, both coherent and
incoherent, for solar and heliospheric radio emission provide us with unique information required
for understanding the basic physical processes operating in natural and laboratory plasmas, at both
microscopic and macroscopic levels. The topics of ongoing intensive investigations are the fundamental problems of plasma astrophysics: the release of magnetic energy, acceleration of charged
particles, magnetohydrodynamic (MHD) waves and turbulence, wave-particle interaction, etc. The
proximity of the Sun to the Earth allows for its study with an unprecedented combination of time,
spatial and spectral resolution, and a unique opportunity to study fundamental plasma physics processes both in situ and remotely. Finally, plasma physics processes in the solar atmosphere are
directly relevant to geophysical challenges such as climate change and space weather; a strong
additional motivation for the intensive development of solar and heliospheric radio physics.
Observations of solar and heliospheric radio emission are mainly performed with dedicated
instruments, such as radio interferometers. However these are rather limited. For example the
highest spatial resolution in the microwave band currently achieved by the Nobeyama Radioheliograph (NoRH, Nakajima et al. 1994), 5" at 34 GHz, is much lower than the spatial scale of plasma
structures in the solar corona as resolved in the EUV and X-ray bands (smaller than 1"). Not even
the upcoming new generation of state-of-the-art specialised solar radio interferometers, namely the
Chinese Spectral Radioheliograph (CSRH, frequency range 0.4–15 GHz, longest baseline 3 km,
Yan et al. 2009), the upgraded Siberian Solar Radio Telescope (SSRT, frequency range 4–8 GHz,
longest baseline 622.3 m, Lesovoi et al. 2014) and the Expanded Owens Valley Solar Array (eOVSA, frequency range 1–18 GHz, longest baseline 1.8 km, Gary et al. 2012) will reach the SKA’s
spatial resolution and sensitivity. In short, as well as providing simultaneously high spectral and
spatial resolution unavailable with current instruments, the SKA will radically (by two orders of
magnitude) improve on their sensitivity, allowing for the detection of a number of physical phenomena predicted theoretically. The breakthrough potential of SKA in solar and heliospheric studies
in the low frequency band has already been demonstrated in frames of the LOw Frequency ARray
(LOFAR) and Murchison Widefield Array (MWA), both of which are SKA pathfinder projects.
These instruments include solar and heliospheric physics, and space weather amongst their key
science objectives and have already lead to several interesting publications (e.g. Mann et al. 2011;
Oberoi et al. 2011; Bowman et al. 2013).
A further interesting opportunity is connected with the fact that for a 300 km baseline, the
proximity of the Sun to the interferometer puts it in the near-field zone of the instrument at higher
frequencies. The sphericity of the waves coming from spatially localised solar sources can be
measured and the radial distance to the source can be estimated, providing us with 3D information:
both angular coordinates on the plane-of-the-sky and the distance to the source (e.g. giving radial
resolution of 0.1 R⊙ at 1.5 GHz on a 300 km baseline, Braun 1997).
For imaging purposes, solar observations are particularly challenging. First of all there is the
immense dynamic range. During major outbursts the flux can be dominated by very spatiallylocalised sources and simultaneously there are elongated features whose brightness temperature
over the same spatial extent as the narrow source could be nine orders of magnitude lower. The
2
THE MOST INTENSIVE GAMMA-RAY FLARE OF QUASAR 3C 279 WITH THE SECOND-ORDER FERMI
ACCELERATION
Katsuaki Asano, and Masaaki Hayashida
Institute for Cosmic Ray Research, The University of Tokyo and
5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582, Japan
(Dated: Submitted; accepted)
ABSTRACT
The very short and bright flare of 3C 279 detected with Fermi-LAT in 2013 December is tested by a
model with stochastic electron acceleration by turbulences. Our time-dependent simulation shows that
the very hard spectrum and asymmetric lightcurve are successfully reproduced by changing only the
magnetic field from the value in the steady period. The maximum energy of electrons drastically grows
by the decrease of the magnetic field, which yields hard photon spectrum as observed. Succeeding
rapid cooling due to the inverse Compton scattering with the external photons reproduces the decaying
feature of the lightcurve. The inferred energy density of the magnetic field is much less than the
electron and photon energy densities. The low magnetic field and short variability timescale are
unfavorable for the jet acceleration model by the gradual Poynting flux dissipation.
Subject headings: acceleration of particles — quasars: individual (3C 279) — radiation mechanisms:
non-thermal — turbulence
1. INTRODUCTION
Multi-wavelength lightcurves of blazar flares show
complex and diversified feature. While in some cases,
there is a time-lag between gamma-ray and X-ray/optical
flares (e.g. Bla˙zejowski et al. 2005; Fossati et al. 2008;
Abdo et al. 2010a; Hayashida et al. 2012), in other
cases an orphan flare in a certain wavelength was detected (e.g. Krawczynski et al. 2004; Abdo et al. 2010b).
Even if a time-dependent model is adopted, such
various behaviors may be difficult to be reproduced
by a one-zone model (Kusunose, Takahara & Li 2000;
Krawczynski, Coppi & Aharonian 2002; Asano et al.
2014). While spatial gradients of the physical parameters in the emission regions (Janiak et al. 2012) may
explain some fraction of the lags, some flares have too
complex spectral evolutions to be modeled even with
a time-dependent multi-zone radiative transfer simulations (Chen et al. 2011). This may imply inhomogeneous
emission regions evolving with a longer timescale than
the dynamical one. Such nontrivial properties in blazar
flare make it difficult to probe physical processes such as
electron acceleration or cooling.
In 2013 December, Fermi Large Area Telescope (LAT)
detected one of the most intense flares in the gammaray band from a flat spectrum radio quasar (FSRQ)
3C 279, reaching ∼ 1 × 10−5 ph cm−2 s−1 for the integrated flux above 100 MeV (Hayashida et al. 2015, hereafter H15). The flux level is comparable to the historical maximum of this source observed at the gamma-ray
band (Wehrle et al. 1998). The gamma-ray flare showed
a very rapid variability with asymmetric time profile with
the shorter rising time of ∼ 2 hrs and the longer falling
time of ∼ 7 hrs. We can expect that this extraordinary
flare was emitted from a sufficiently compact region that
can be regarded as homogeneous differently from other
usual flares. In this case, the decaying timescale may [email protected], [email protected]
rectly correspond to the cooling timescale, and the flare
is an ideal target to discuss the physical processes.
Another important property in this flare of 3C 279,
a very hard photon index of Γγ = 1.7 ± 0.1 was observed in the > 100 MeV band by Fermi-LAT. Such a
hard photon index has been rarely observed in FSRQs,
whose luminosity peak by inverse-Compton (IC) scattering is usually located below 100 MeV. While the mean
of the Γγ distribution is FSRQs corresponds to about
2.4 (Ackermann et al. 2015), hard photon indices Γγ < 2
have been occasionally observed in some bright FSRQs
only during rapid flaring events (Pacciani et al. 2014). In
order to reproduce the hard photon index by IC scattering in the fast cooling regime, the index of parent electrons should be much harder than 2, which can hardly
be generated in a normal shock acceleration process. In
addition, the flare event of 3C 279 indicates a high Compton dominance parameter Lγ /Lsyn > 300, leading to extremely low jet magnetization with LB /Lj . 10−4 (H15).
To explain the flare event of 3C 279, rather than
assuming prompt electron injection by the shock
acceleration, we propose the stochastic acceleration
(SA) model, which is phenomenologically equivalent to the second-order Fermi acceleration (FermiII, e.g. Katarzy´
nski et al. 2006; Stawarz & Petrosian
2008; Lefa, Rieger & Aharonian 2011, and references
therein). The SA may be drived by magnetic reconnection (Lazarian et al. 2012). Otherwise, hydrodynamical turbulences that drive the acceleration are possibly
induced via the Kelvin–Helmholtz instability as an axial mode (e.g. Mizuno, Hardee & Nishikawa 2007), or the
Rayleigh–Taylor and Richtmyer–Meshkov instabilities as
radial modes (Matsumoto & Masada 2013). Broadband
spectra of blazars in the steady state have been successfully fitted with recent SA models (Asano et al. 2014;
Diltz & Böttcher 2014; Kakuwa et al. 2015). The flare
state should be also tested with such models to show the
wide-range applicability of the SA. This is the first at-
NORDITA-2015-83
Evolution of Primordial Magnetic Fields: From Generation Till Today
Tina Kahniashvili∗
The McWilliams Center for Cosmology and Department of Physics,
Carnegie Mellon University, 5000 Forbes Ave, Pittsburgh, PA 15213, USA
Department of Physics, Laurentian University,
Ramsey Lake Road, Sudbury, ON P3E 2C, Canada and
Abastumani Astrophysical Observatory, Ilia State University,
3-5 Cholokashvili Avenue, Tbilisi, 0162, Georgia
Axel Brandenburg†
Nordita, KTH Royal Institute of Technology and Stockholm University,
Roslagstullsbacken 23, 10691 Stockholm, Sweden and
Department of Astronomy, AlbaNova University Center,
Stockholm University, 10691 Stockholm, Sweden
Alexander G. Tevzadze‡
Faculty of Exact and Natural Sciences, Tbilisi State University,
3 Chavchavadze Avenue, Tbilisi, 0179, Georgia and
Abastumani Astrophysical Observatory, Ilia State University,
3-5 Cholokashvili Avenue, Tbilisi, 0162, Georgia
Abstract
In this presentation we summarize our previous results concerning the evolution of primordial magnetic fields with
and without helicity during the expansion of the Universe. We address different magnetogenesis scenarios such as
inflation, electroweak and QCD phase transitions magnetogenesis. A high Reynolds number in the early Universe
ensures strong coupling between magnetic field and fluid motions. After generation the subsequent dynamics of the
magnetic field is governed by decaying hydromagnetic turbulence. We claim that primordial magnetic fields can be
considered as a seeds for observed magnetic fields in galaxies and clusters. Magnetic field strength bounds obtained
in our analysis are consistent with the upper and lower limits of extragalactic magnetic fields.
∗
Electronic address: [email protected]
‡
†
1
Effect of Stellar Encounters on Comet Cloud Formation
A. Higuchi
arXiv:1507.00502v1 [astro-ph.EP] 2 Jul 2015
Department of Earth and Planetary Sciences, Faculty of Science, Tokyo Institute of
Technology, Meguro, Tokyo 152-8551
and
E. Kokubo
Division of Theoretical Astronomy, National Astronomical Observatory of Japan, Mitaka,
Tokyo 181-8588
Received
;
accepted
–2–
ABSTRACT
We have investigated the effect of stellar encounters on the formation and
disruption of the Oort cloud using the classical impulse approximation. We calculate the evolution of a planetesimal disk into a spherical Oort cloud due to
the perturbation from passing stars for 10 Gyr. We obtain the empirical fits
of the e-folding time for the number of Oort cloud comets using the standard
exponential and Kohlrausch formulae as functions of the stellar parameters and
the initial semimajor axes of planetesimals. The e-folding time and the evolution
timescales of the orbital elements are also analytically derived. In some calculations, the effect of the Galactic tide is additionally considered. We also show the
radial variations of the e-folding times to the Oort cloud. From these timescales,
we show that if the initial planetesimal disk has the semimajor axes distribution
dn/da ∝ a−2 , which is produced by planetary scattering (Higuchi et al. 2006),
the e-folding time for planetesimals in the Oort cloud is ∼10 Gyr at any heliocentric distance r. This uniform e-folding time over the Oort cloud means that the
supply of comets from the inner Oort cloud to the outer Oort cloud is sufficiently
effective to keep the comet distribution as dn/dr ∝ r −2 . We also show that
the final distribution of the semimajor axes in the Oort cloud is approximately
proportional to a−2 for any initial distribution.
Subject headings: Oort Cloud — comets: general
Distributed image reconstruction for
very large arrays in radio astronomy
André Ferrari, David Mary, Rémi Flamary and Cédric Richard
arXiv:1507.00501v1 [astro-ph.IM] 2 Jul 2015
Laboratoire Joseph-Louis Lagrange
Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d’Azur
Nice, France
Email: [email protected]
Abstract—Current and future radio interferometric arrays such as
LOFAR and SKA are characterized by a paradox. Their large number
of receptors (up to millions) allow theoretically unprecedented high
imaging resolution. In the same time, the ultra massive amounts of
samples makes the data transfer and computational loads (correlation
and calibration) order of magnitudes too high to allow any currently
existing image reconstruction algorithm to achieve, or even approach, the
theoretical resolution. We investigate here decentralized and distributed
image reconstruction strategies which select, transfer and process only
a fraction of the total data. The loss in MSE incurred by the proposed
approach is evaluated theoretically and numerically on simple test cases.
I. I NTRODUCTION
Since the commissioning of the first large radio interferometers in
the 70s and 80s (such as the VLA in the USA and the WSRT) radio
astronomy in the range of large wavelengths has grown dramatically,
particularly with the development of more and more extended antenna
arrays. In the prospect of the most sensitive radio telescope ever
built, the SKA which will be operational in the 2020s, several new
generation radio telescopes are being built or planned (LOFAR in the
Netherlands, ASKAP and the Murchison Widefield Array Australia,
e-MERLIN in the UK, e-EVN based in Europe, MeerKAT in South
Africa, JVLA the United States).
As an example, LOFAR consists of 48 groups of antennas (stations), among which approximately 35,000 elementary antennas are
located in the Netherlands. The “superterp”, the heart of LOFAR
is a super-station: a cluster of six stations. Eight other stations,
totalizing approximately 13,000 antennas are located in the surrounding countries. A project of a new super-station in Nançay
(F) is under consideration. Within each station, antennas form a
phased array which allows for digital beamforming simultaneously
in several directions and frequency bands. The beam-formed data
from the stations are centralized at the University of Groningen
in the Netherlands where a supercomputer is responsible for the
combination of the beam data from all stations. The resulting data
are then stored on a cluster of ASTRON, the Netherlands Institute
for Radio Astronomy, where the images (and other deliverables)
are reconstructed. As a mean of comparison SKA will totalize 2.5
millions antennas, with a square kilometer collecting area distributed
over an area of ≈ 5,000 km diameter.
Beyond specific objectives that distinguish these new fully digital
“software telescopes”, they are all characterized by a great flexibility.
Another common point is the amount of data which must be transferred to the central computer and processed. It amounts to 1 terabit/second for LOFAR and will be of the order of 14 exabyte/day
This work was supported by CNRS grant MASTODONS; DISPLAY
project.
for SKA (more than 100 times the global internet traffic). LOFAR
uses a 1.5 Blue Gene/P for the data reduction and the computation of
correlations. IBM et ASTRON will develop by 2024 a supercomputer
to process and store 1 petabytes of data everyday [2].
This correspondence investigates the possibility to distribute the
image reconstruction over the super-stations. The main objective is
to avoid centralization of the sampled electromagnetic fields acquired
by all stations in order to reduce the data transfer and the exponential
increase in the calibration and computational load.
Section II recalls the basis of radio astronomy with aperture
synthesis and proposes a strategy where each super-station uses all
its antenna and one reference signal from the other super-stations.
The loss of performances that follows is evaluated on a simple
model using the Cramér Rao Lower Bound (CRLB). Section III
shows that the image reconstruction problem can be written as a
global variable consensus problem with regularization. Numerical
simulations illustrate the performances of the proposed approach. A
concluding section presents perpectives.
II. A PERTURE SYNTHESIS FOR RADIO ASTRONOMY
A. Standard aperture synthesis model
This section provides the basic equations of radio astronomy
with multiple sensor array and describes a partial aperture synthesis
strategy which aims to reduce data transfer, allowing a decentralized
image reconstruction.
To simplify the notations and without loss of generality, we will
not make explicit the wavelengths dependence and the Earth rotation
and assume punctual antennas. The coordinates of the stations (within
each station, a beam is created from the phased array) in a plane
perpendicular to the line of sight are denoted as r j and the map
of interest (the “image” of a region of the sky) is x(p) where p
denotes the angular coordinates on the sky. The fundamental equation
of interferometry relates the Fourier transform of the map to the
spatial coherency (visibility) of the incoming electromagnetic field.
A measurement of the coherency is obtained by correlating the signal
acquired by a pair of stations (i, j) properly delayed located at r i
and r j , giving in the noiseless case a point of visibility at spatial
frequency u` = r j − r i :
Z
t
v(u` ) = x(p)e−2πu` p dp
(1)
See for example [9], [10] for a comprehensive description of radio
astronomy and signal processing related tools.
Computation of v(u` ) obviously requires the transfer of signals
from stations i and j in the same place. The stations are normally grouped in “super-stations” (e.g. the superterp for LOFAR)
accounting for low frequencies (kr i − r j k2 small). Resolution is
ANNz2 - Photometric redshift and probability density
function estimation using machine learning methods
I. Sadeh1,2⋆ , F. B. Abdalla1,3 and O. Lahav1
1 Department
of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK
D-15735 Zeuthen, Germany
3 Department of Physics and Electronics, Rhodes University, PO Box 94, Grahamstown, 6140, South Africa
2 DESY-Zeuthen,
1 July 2015
ABSTRACT
We present ANNz2, a new implementation of the public software for photometric redshift (photo-z) estimation of Collister and Lahav (2004). Large photometric galaxy
surveys are important for cosmological studies, and in particular for characterizing
the nature of dark energy. The success of such surveys greatly depends on the ability to measure photo-zs, based on limited spectral data. ANNz2 utilizes multiple machine learning methods, such as artificial neural networks, boosted decision/regression
trees and k-nearest neighbours. The objective of the algorithm is to dynamically optimize the performance of the photo-z estimation, and to properly derive the associated
uncertainties. In addition to single-value solutions, the new code also generates full
probability density functions (PDFs) in two different ways. In addition, estimators are
incorporated to mitigate possible problems of spectroscopic training samples which are
not representative or are incomplete. ANNz2 is also adapted to provide optimized solutions to general classification problems, such as star/galaxy separation. We illustrate
the functionality of the code using data from the tenth data release of the Sloan Digital
Sky Survey and the Baryon Oscillation Spectroscopic Survey. The code is available for
download at https://github.com/IftachSadeh/ANNZ .
Key words: Photometric redshifts, star/galaxy separation, machine learning methods.
1
INTRODUCTION
Redshifts, usually denoted by z, effectively provide a third,
radial dimension to Cosmological analyses. They allow the
study of phenomena as a function of distance and time, as
well as enable the identification of large structures, such
as galaxy clusters. The current and next generations of
dark energy experiments, such as the Dark Energy Survey (DES), the Large Synoptic Survey Telescope (LSST)
and the Euclid experiment1 will observe a few billion galaxies. Redshifts may be measured with great precision using
spectroscopy. However, it is infeasible to obtain spectra for
such large galaxy samples. The success of these imaging surveys is therefore critically dependent on the measurement of
high-quality photometric redshifts (photo-zs). For instance,
a benchmark of LSST is to measure the dark energy equation of state parameter, w, with per-cent level uncertainty.
This is expected to be achievable with weak-lensing tomography (Hu 1999; Zhan and Knox 2006). However, it will require a precision of ∼ 0.002 · (1 + z) in determination of the
systematic bias in the redshift.
This paper presents ANNz2, a new implementation of
the popular code of Collister and Lahav (2004), which uses
artificial neural networks to estimate photometric redshifts.
ANNz2 is free and publicly available2 ; the code has already
been incorporated as part of the analysis chain of the
anchez et al. 2014), and is planned to be included
DES (S´
in the software pipeline of Euclid.
The new code incorporates a variety of machine learning
techniques in addition to artificial neural networks. It has
been designed to calculate both photometric redshifts and
photo-z probability density functions (PDFs), doing so in
several different ways. The introduction of photo-z PDFs
has been shown to improve the accuracy of cosmological
⋆
E-mail: [email protected] .
See http://www.darkenergysurvey.org , http://www.lsst.org
and http://sci.esa.int/euclid/ .
1
2
See https://github.com/IftachSadeh/ANNZ .
Detailed photospheric abundances of 28 Peg and
HD 202240✩
¨
Aslı Elmaslı, S¸eyma C
¸ alı¸skan, Tolgahan Kılı¸co˘glu∗, K¨
ubraözge Unal,
Yahya
Nasolo, and Berahitdin Albayrak
Department of Astronomy and Space Sciences, Ankara University, 06100, Tando˘gan,
Ankara, Turkey
Abstract
The atmospheric parameters and chemical abundances of two neglected Atype stars, 28 Peg and HD 202240, were derived using high resolution spectra
¨ ITAK
˙
obtained at the TUB
National Observatory. We determined the photospheric abundances of eleven elements for 28 Peg and twenty for HD 202240,
using equivalent-width measurement and spectral synthesis methods. Their
abundance patterns are in good agreement with those of chemically normal
A-type stars having similar atmospheric parameters. We pinpoint the position of these stars on the H-R diagram and estimate their masses and ages
as; 2.60 ± 0.10 M⊙ and 650 ± 50 Myr for 28 Peg and 4.50 ± 0.09 M⊙ and
150 ± 10 Myr for HD 202240. To compare our abundance determinations
with those of stars having similar ages and atmospheric parameters, we select members of open clusters. We notice that our target stars exhibit similar
abundance patterns with these members.
✩
¨ ITAK
˙
Based on observations made at the TUB
National Observatory, Turkey (Program
ID 09BRTT150-477-0).
∗
Corresponding author. Tel.: +90 312 212 67 20; fax +90 312 223 23 95
Email address: [email protected] (Tolgahan Kılı¸co˘glu)
Preprint submitted to New Astronomy
July 3, 2015
Published in Astronomy Letters, 2015, Vol. 41, No. 8, pp. 383-393.
Variation of the baryon-to-photon ratio
due to decay of dark matter particles
E. O. Zavarygin1,2⋆ and A. V. Ivanchik1,2⋆⋆
1
2
Ioffe Institute, ul. Politekhnicheskaya 26, St. Petersburg, 194021 Russia
Peter the Great St.Petersburg Polytechnic University, ul. Politekhnicheskaya 29, St. Petersburg, Russia
Received 05 December, 2014
Abstract
The influence of dark matter particle decay on the baryon-to-photon ratio has been studied for different cosmological epochs. We consider different parameter values of dark matter particles such as mass, lifetime, the relative
fraction of dark matter particles. It is shown that the modern value of the dark matter density ΩCDM = 0.26 is
enough to lead to variation of the baryon-to-photon ratio up to ∆η/η ∼ 0.01 ÷ 1 for decays of the particles with
masses 10 GeV ÷ 1 TeV. However, such processes can also be accompanied by emergence of an excessive gamma
ray flux. The observational data on the diffuse gamma ray background are used to making constraints on the
dark matter decay models and on the maximum possible variation of the baryon-to-photon ratio ∆η/η . 10−5 .
Detection of such variation of the baryon density in future cosmological experiments can serve as a powerful
means of studying properties of dark matter particles.
Key words. cosmology, dark matter, baryonic matter
1. INTRODUCTION
In the last decade, cosmology has passed into the category of precision sciences. Many cosmological parameters are currently determined with a high precision that
occasionally reaches fractions of a percent (Ade et al.
2014). One of such parameters is the baryon-to-photon
ratio η ≡ nb /nγ , where nb and nγ are the baryon and
photon number densities in the Universe, respectively.
In the standard cosmological model, the present value
of η is assumed to have been formed upon completion of
electron-positron annihilation several seconds after the
Big Bang and has not changed up to now.
The value of nγ associated with the cosmic microwave background (CMB) photons is defined by the
well-known relation
3
3
T
2ζ(3) kT
= 410.73
cm−3 ,
nγ =
π2
~c
2.7255 K
where ζ(x) is the Riemann zeta function, k is the
Boltzmann constant, ~ is the Planck constant, c is the
speed of light, and T is the CMB temperature at the
corresponding epoch. The CMB temperature is currently determined with a high accuracy and is T0 =
2.7255(6) K at the present epoch (Fixsen 2009); for other
epochs, it is expressed by the relation T = T0 (1 + z),
where z is the cosmological redshift at the corresponding
epoch. Thus, given nγ , a relation between the parameter
η and Ωb , the relative baryon density in the Universe,
can be obtained (Steigman 2006):
η = 273.9 × 10−10 Ωb h2 ,
⋆
⋆⋆
where h = 0.673(12) is the dimensionless Hubble parameter at the present epoch (Ade et al. 2014). According
to present views, the baryon density, which is the density of ordinary matter (atoms, molecules, planets and
stars, interstellar and intergalactic gases), does not exceed 5% of the entire matter filling the Universe, while
95% of the density in the Universe is composed of unknown forms of matter/energy that manifest themselves
(for the time being) gravitationally (see, e.g., Gorbunov
and Rubakov 2008).
At present, observations allow Ωb to be independently estimated for four cosmological epochs:
(i) the epoch of Big Bang nucleosynthesis (zBBN ∼ 109 ;
see, e.g., Steigman et al. 2007);
(ii) the epoch of primordial recombination (zPR ≃ 1100;
see, e.g., Ade et al. 2014);
(iii) the epoch associated with the Lyα forest (z ∼ 2 ÷ 3;
i.e., ∼10 Gyr ago; see, e.g., Rauch 1998; Hui et al. 2002);
(iv) the present epoch (z = 0; see, e.g., Fukugita and
Peebles 2004).
For the processes at the epochs of Big Bang nucleosynthesis and primordial recombination, η is one of
the key parameters determining their physics. For these
epochs, the methods of estimating η, (i) comparing the
observational data on the relative abundances of the
primordial light elements (D, 4 He, 7 Li) with the predictions of the Big Bang nucleosynthesis theory and (ii)
analyzing the CMB anisotropy, give the most accurate
estimates of η to date that coincide, within the observational error limits: ηBBN = (6.0±0.4)×10−10 (Steigman
2007) and ηCMB = (6.05±0.07)×10−10 (Ade et al. 2014).
This argues for the correctness of the adopted model of
the Universe and for the validity of the standard physics
used in theoretical calculations. However, it should be
noted that at present, as the accuracy of observations
Accepted by The Astrophysical Journal
ELLERMAN BOMBS AT HIGH RESOLUTION III. SIMULTANEOUS OBSERVATIONS WITH IRIS AND SST
G. J. M. Vissers1 , L. H. M. Rouppe van der Voort1 , R. J. Rutten2,1 , M. Carlsson1 , and B. De Pontieu3,1
1 Institute
of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315 Oslo, Norway; [email protected]
2 Lingezicht Astrophysics, ’t Oosteneind 9, 4158CA Deil, The Netherlands and
3 Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Bldg. 252, Palo Alto, CA 94304, USA
Draft version Friday 3rd July, 2015
ABSTRACT
Ellerman bombs are transient brightenings of the extended wings of the solar Balmer lines in emerging active regions. We describe their properties in the ultraviolet lines sampled by the Interface Region
Imaging Spectrograph (IRIS), using simultaneous imaging spectroscopy in Hα with the Swedish 1m Solar Telescope (SST) and ultraviolet images from the Solar Dynamics Observatory for Ellerman
bomb detection and identification. We select multiple co-observed Ellerman bombs for detailed analysis. The IRIS spectra strengthen the view that Ellerman bombs mark reconnection between bipolar
kilogauss fluxtubes with the reconnection and the resulting bi-directional jet located within the solar
photosphere and shielded by overlying chromospheric fibrils in the cores of strong lines. The spectra
suggest that the reconnecting photospheric gas underneath is heated sufficiently to momentarily reach
stages of ionization normally assigned to the transition region and the corona. We also analyze similar outburst phenomena that we classify as small flaring arch filaments and ascribe to higher-located
reconnection. They have different morphology and produce hot arches in million-Kelvin diagnostics.
Subject headings: Sun: activity – Sun: atmosphere – Sun: magnetic fields
1. INTRODUCTION
Ellerman (1917) discovered intense short-lived brightenings of the extended wings of the Balmer Hα line at
6563 ˚
A that he called “solar hydrogen bombs”. They are
called Ellerman bombs (henceforth EB) since McMath
et al. (1960). For more detail we refer to the excellent
summary by Georgoulis et al. (2002) and our more recent review of the extensive EB literature in Rutten et al.
(2013).
We discuss the subsequent EB literature below, but
here point out the recent discovery by Peter et al. (2014)
of very hot “bombs” in ultraviolet spectra from the Interface Region Imaging Spectrograph (IRIS, De Pontieu
et al. 2014). The present paper addresses their suggestion that these bombs might have been EBs or similar to
EBs.
A major motivation to study EBs is that they supposedly mark locations of serpentine flux rope emergence
in newly emerging active regions (e.g., Bernasconi et al.
2002; Pariat et al. 2004; Isobe et al. 2007; Archontis
& Hood 2009; Pariat et al. 2009). Understanding their
nature may therefore present a way to measure active
region evolution, in particular the reconnective field topography evolution that eventually produces much larger
solar outbursts. In this context, EBs should become useful as telltales of strong-field reconnection when well understood.
In addition, the complex physics and spectrum formation of the EB phenomenon are of interest per sé since
EBs appear to be pockets of hot gas within the photosphere. The discovery of extremely hot IRIS bombs
by Peter et al. (2014) that also appear to be photospheric enhances this interest. In our present series of EB
analyses we employ high-quality imaging spectroscopy
with the Swedish 1-m Solar Telescope (SST; Scharmer
et al. 2003) to study EBs at unprecedented spatial, spectral, and temporal resolution. Paper I (Watanabe et al.
2011) established that EBs are a purely photospheric
phenomenon.
Paper II (Vissers et al. 2013) added evidence that EBs
mark magnetic reconnection of strong opposite-polarity
field concentrations in the low photosphere and discussed
their appearance in 1700 ˚
A images from the Atmospheric
Imaging Assembly (AIA; Lemen et al. 2012) of the Solar
Dynamics Observatory (SDO).
Let us morphologically define the three bomb-like phenomena that we discuss below, based on our inspections
of dozens of such features in SST, SDO, and IRIS data.
More detail on their recognition is given in Sect. 2.
We define “Ellerman bombs” (EB) as substantial
brightenings of the extended wings of Hα without core
brightening that, at sufficient angular and temporal
resolution, show definite rapid-flame morphology when
viewed from aside as described in Paper I. EB Hα
wing brightenings exceed those from much more ubiquitous magnetic concentrations that happen to also appear bright in the Hα wings (“pseudo-EBs”, Rutten et al.
2013).
Next, we define “flaring arch filaments” (henceforth
FAFs) as sudden fierce brightenings in AIA 1600 ˚
A image
sequences that differ from the EB brightenings also seen
in this AIA channel by appearing with shorter duration
and more abrupt changes, having elongated morphology,
and showing fast apparent brightness motion along filamentary strands. Because they are usually much less
evident in AIA 1700 ˚
A images, their 1600 ˚
A appearance
is likely due to brightening of the C iv doublet at 1548
and 1550 ˚
A in AIA’s 1600 ˚
A passband. Their filamentary
morphology and rapid evolution suggest that these are
heating events, likely reconnection, that take place along
the fibrilar canopy seen e.g., at Hα line center, or eject
heated matter along chromospheric field lines.
Finally, we define “IRIS bombs” (henceforth IBs) following Peter et al. (2014) as ultraviolet brightenings with
substantial emission in the Si iv lines observed by IRIS,
and showing these with very wide and complex non-
Astronomy & Astrophysics manuscript no. CaTcal˙v14
July 3, 2015
© ESO 2015
The Calcium Triplet metallicity calibration for galactic bulge stars. ⋆
S. Vásquez1,2 , M. Zoccali1,2 , V. Hill3 , O. A. Gonzalez4 , I. Saviane4 , M. Rejkuba5 , and G. Battaglia6,7
1
2
3
4
5
6
7
Instituto de Astrof´ısica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
Laboratoire Lagrange (UMR7293), Université de Nice Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, CS34229, 06304,
Nice Cedex 04, France
European Southern Observatory, Av. Alonso de Cordova 3107, Casilla 19, 19001, Santiago, Chile
European Southern Observatory, Karl-Schwarzschild Strasse 2, D-85748 Garching, Germany
Instituto de Astrof´ısica de Canarias, calle via Láctea s/n, 38205 San Cristobal de La Laguna, Tenerife, Spain
Universidad de La Laguna, Dpto. Astrof´ısica, 38206 La Laguna, Tenerife, Spain
Preprint online version: July 3, 2015
ABSTRACT
Aims. We present a new calibration of the Calcium II Triplet equivalent widths versus [Fe/H], constructed upon K giant stars in the
Galactic bulge. This calibration will be used to derive iron abundances for the targets of the GIBS survey, and in general it is especially
suited for solar and supersolar metallicity giants, typical of external massive galaxies.
Methods. About 150 bulge K giants were observed with the GIRAFFE spectrograph at VLT, both at resolution R∼20,000 and at
R∼6,000. In the first case, the spectra allowed us to perform direct determination of Fe abundances from several unblended Fe lines,
deriving what we call here high resolution [Fe/H] measurements. The low resolution spectra allowed us to measure equivalent widths
of the two strongest lines of the near infrared Calcium II triplet at 8542 and 8662 Å.
Results. By comparing the two measurements we derived a relation between Calcium equivalent widths and [Fe/H] that is linear over
the metallicity range probed here, −1 <[Fe/H]< +0.7. By adding a small second order correction, based on literature globular cluster
data, we derived the unique calibration equation [Fe/H]CaT = −3.150 + 0.432W ′ + 0.006W ′2 , with a rms dispersion of 0.197 dex, valid
across the whole metallicity range −2.3 <[Fe/H]< +0.7.
Key words. Stars: abundances – Galaxy: bulge – Techniques: spectroscopic
1. Introduction
The Calcium II Triplet (CaT) at ∼8500 Å is one of the most
widely used metallicity index, as well as an excellent feature
to measure radial velocity at low spectral resolution. The three
lines at λ8498, λ8542, λ8662 Å are so strong that they can be
measured easily at low resolution and at relatively low signal
to noise. In addition, their location in the near-infrared part of
the spectrum is ideal to observe the brightest stars of any not
too young stellar population, namely cool giants. CaT spectra
of cool giants can be obtained with reasonable exposure time
both for external galaxies in the local group, too far away to be
observed at high spectral resolution, and for Milky Way stars in
high extinction regions, such as the Galactic bulge.
Obviously the popularity of the CaT spectral feature resides in how accurately it can be used to measure metallicities.
Armandroff & Zinn (1988) first demonstrated that the equivalent
widths (EWs) of CaT lines, in the integrated spectra of globular clusters (GCs), strongly correlated with the cluster metallicity [Fe/H]. A few years later, Olszewski et al. (1991) and
Armandroff & Da Costa (1991) analyzed the behaviour of CaT
lines in individual cluster stars. They noticed that the EWs of
CaT lines show a dependence not only on metallicity, but also
on absolute magnitude. They therefore introduced the use of “reduced equivalenth widths” (W ′ ), which corresponds to the sum
⋆
Based on observations taken with ESO telescopes at the La Silla
Paranal Observatory under programme ID 385.B-0735(B).
of some combination of the individual EWs, weighed by the difference between the star V magnitude and the magnitude of the
Horizontal Branch in the same cluster (V − VHB ).
Several empirical relations between the reduced EWs of CaT
lines and the [Fe/H] abundance are present in the literature. Most
of them used star clusters, for which [Fe/H] abundance could be
derived in several ways, and not necessarily for the same stars for
which CaT was measured. Among those, a very comprehensive
one is the work of Rutledge et al. (1997) who derived CaT metallicities for 52 Galactic GCs in a homogeneous scale, covering
the range −2 <[Fe/H]< −0.7. By comparing their scale with the
classical Zinn & West (1984) metallicity scale, they found a nonlinear relation between the two. Conversely, a linear relation was
found between the CaT metallicities by Rutledge et al. (1997)
and the metallicities derived by Carretta & Gratton (1997). The
latter are based on Fe lines, measured on high resolution spectra.
Traditionally, the CaT metallicity calibration has been constructed based on RGB stars in globular (Cole et al. 2004;
Warren & Cole 2009; Saviane et al. 2012, e.g.) or open clusters
(Carrera et al. 2007, 2013) Open clusters allowed Carrera et al.
to extend the metallicity range up to [Fe/H]∼+0.5, at the same
time probing a younger age regime (13 Gyr<age<0.25 Gyr).
The CaT EWs seem to be only weakly dependent on the age of
the star, although only a few star clusters constrain the relation
at high metallicity, and anyway old star clusters at supersolar
metallicities are not available to set a robust constrain on the age
dependance.
1
Draft version 2015.7.3.24
PHYSICAL DUST MODELS FOR THE EXTINCTION TOWARD SUPERNOVA 2014J IN M82
Jian Gao1,2 , B. W. Jiang1 , Aigen Li2 , Jun Li1 , and Xiaofeng Wang3
Draft version 2015.7.3.24
ABSTRACT
Type Ia supernovae (SNe Ia) are powerful cosmological “standardizable candles” and the most
precise distance indicators. However, a limiting factor in their use for precision cosmology rests on
our ability to correct for the dust extinction toward them. SN 2014J in the starburst galaxy M82,
the closest detected SN Ia in three decades, provides unparalleled opportunities to study the dust
extinction toward an SN Ia. In order to derive the extinction as a function of wavelength, we model
the color excesses toward SN 2014J, which are observationally derived over a wide wavelength range
in terms of dust models consisting of a mixture of silicate and graphite. The resulting extinction laws
steeply rise toward the far ultraviolet, even steeper than that of the Small Magellanic Cloud (SMC).
We infer a visual extinction of AV ≈ 1.9 mag, a reddening of E(B − V ) ≈ 1.1 mag, and a totalto-selective extinction ratio of RV ≈ 1.7, consistent with that previously derived from photometric,
spectroscopic, and polarimetric observations. The size distributions of the dust in the interstellar
medium toward SN 2014J are skewed toward substantially smaller grains than that of the Milky Way
and the SMC.
Subject headings: dust, extinction — galaxies: ISM — galaxies: individual (Messier 82) — supernovae:
individual (SN 2014J)
1. INTRODUCTION
Type Ia supernovae (SNe Ia) are considered to be one
of the most precise tools for determining astronomical
distances (Howell 2011). Because of their high luminosity and relatively small dispersion at the maxima of their
bolometric light curves, they are commonly utilized as
cosmological “standardizable candles”. The accelerated
expansion of the Universe and the presence of dark energy were discovered through SNe Ia used as standardizable candles (Riess et al. 1998; Perlmutter et al. 1999).
The effectiveness of SNe Ia as distance indicators and
standard candles is hampered by the systematic uncertainties related to their explosion mechanism and progenitor systems, and more importantly, the line-of-sight
extinction. The distance d measured in parsec to a SN
is lg d = 0.2 (mλ − Mλ + 5 − Aλ ), where mλ and Mλ are
its apparent and absolute magnitudes at wavelength λ,
and Aλ is the extinction. As it is not easy to directly
measure Aλ , one often measures the color excess (or reddening) E(λ−V ) ≡ Aλ −AV , where AV is the extinction
in the V-band (centered around 5500 ˚
A). SN reddening
is often measured by comparing the observed SN colors
to a zero-reddening locus.
Cardelli et al. (1989; CCM) found that the Galactic extinction curves (or extinction laws) — the wave1 Department of Astronomy, Beijing Normal University,
Beijing 100875, China; [email protected], [email protected]
2 Department of Physics and Astronomy, University of
Missouri, Columbia, MO 65211, USA; [email protected]
3 Department
of Physics,
and Center for Astrophysics,
Tsinghua University,
Beijing 100084,
China
wang− [email protected]
length dependencies of the extinction — can be closely
parametrized by the total-to-selective extinction ratio
RV ≡ AV /E(B − V ), where the B-band centers around
4400 ˚
A (also see Fitzpatrick 1999, hereafter FTZ). Astronomers often derive RV for SNe Ia by fitting the observed E(λ − V ) with the RV -based CCM formula. Once
RV is determined, one can apply the CCM-formula (or
some other parameterizations) to derive Aλ . However,
we caution that the CCM- and FTZ-parameterizations
have been derived for Galactic sightlines with 2 < RV <
5, and may not be valid for external galaxies. Note that
the CCM formula is not even applicable to the Large
and Small Magellanic Clouds (LMC, SMC; Gordon et al.
2003).
SNe Ia are so rare that nearby SNe Ia (d < 5 Mpc) are
detected only about once a decade. SN 2014J, discovered in the nearby starburst galaxy M82 at a distance of
d ≈ 3.5 Mpc (Dalcanton et al. 2009), is the nearest SN
Ia seen in the last three decades. Its proximity offers an
unprecedented opportunity to study the extinction and
reddening toward a SN Ia. The aim of this Letter is to derive RV and Aλ by fitting the reddening curve obtained
by Amanullah et al. (2014) during the epoch range of
[−5, +5] days around its peak brightness (§2) using the
silicate-graphite model (§3). The results are presented in
§3, discussed in §4, and summarized in §5.
2. COLOR-EXCESS CURVES OF SN 2014J
Various studies have been carried out to determine the
RV value for the sightline toward SN 2014J (e.g., see
Amanullah et al. 2014; Foley et al. 2014; Goobar et al.
2014; Marion et al. 2015; Welty et al. 2014).
More
specifically, based on the UV to near-IR photometry of
Printed 3 July 2015
Automated Kinematic Modelling of Warped Galaxy Discs
in Large Hi Surveys: 3D Tilted Ring Fitting of HI
Emission Cubes.
P. Kamphuis1∗, G. I. G. Józsa2,3,4, S-.H. Oh5,6, K. Spekkens7 , N. Urbancic7,
P.
Serra1, B. S. Koribalski1, R.-J. Dettmar8.
1
CSIRO Astronomy & Space Science, Australia Telescope National Facility, P.O. Box 76, Epping, NSW 1710, Australia
South Africa, Radio Astronomy Research Group, 3rd Floor, The Park, Park Road, Pinelands, 7405, South Africa
3 Rhodes University, Department of Physics and Electronics, Rhodes Centre for Radio Astronomy Techniques & Technologies,
PO Box 94, Grahamstown, 6140, South Africa
4 Argelander-Institut f¨
ur Astronomie, Universit¨
at Bonn, Auf dem H¨
ugel 71, 53121 Bonn, Germany
5 International Centre for Radio Astronomy Research (ICRAR), Univ. of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia
6 ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), 44-70 Rosehill Street, Redfern NSW 2016, Sydney, Australia
7 Department of Physics, Royal Military College of Canada, P.O. Box 17000, Station Forces, Kingston, Ontario K7K 7B4, Canada
8 Astronomisches Institut Ruhr-Universit¨
at Bochum, Universit¨
atstrasse 150, D-44801 Bochum, Germany
2 SKA
ABSTRACT
Kinematical parameterisations of disc galaxies, employing emission line observations,
are indispensable tools for studying the formation and evolution of galaxies. Future
large-scale Hi surveys will resolve the discs of many thousands of galaxies, allowing
a statistical analysis of their disc and halo kinematics, mass distribution and dark
matter content.
Here we present an automated procedure which fits tilted-ring models to Hi data
cubes of individual, well-resolved galaxies. The method builds on the 3D Tilted Ring
Fitting Code (TiRiFiC) and is called FAT (Fully Automated TiRiFiC).
To assess the accuracy of the code we apply it to a set of 52 artificial galaxies
and 25 real galaxies from the Local Volume Hi Survey (LVHIS). Using LVHIS data,
we compare our 3D modelling to the 2D modelling methods DiskFit and rotcur.
A conservative result is that FAT accurately models the kinematics and the
morphologies of galaxies with an extent of eight beams across the major axis in the
inclination range 20◦ -90◦ without the need for priors such as disc inclination. When
comparing to 2D methods we find that velocity fields cannot be used to determine
inclinations in galaxies that are marginally resolved. We conclude that with the
current code tilted-ring models can be produced in a fully automated fashion. This
will be essential for future Hi surveys, with the Square Kilometre Array and its
pathfinders, which will allow us to model the gas kinematics of many thousands of
well-resolved galaxies. Performance studies of FAT close to our conservative limits,
as well as the introduction of more parameterised models will open up the possibility
to study even less resolved galaxies.
Key words: galaxies: ISM, galaxies: kinematics and dynamics, galaxies: structure,
methods: data analysis, surveys
1
INTRODUCTION
The accurate description of the kinematics of galaxies is crucial to get insight into how they form and evolve during their
∗ E-mail: [email protected]
c 2013 RAS
lifetimes. The Doppler-shifted Hi line is one of the main tracers of these kinematics; Hi is ubiquitous, largely unaffected
by absorption and often extends far further out than other
probes. As such, parameterisation of the Hi distribution and
dynamics has been done for several decades, mostly on an
individual galaxy basis and in a highly interactive fashion.
Equations of state in the Hartle–Thorne model of neutron stars
selecting acceptable variants of the resonant switch model of twin
HF QPOs in the atoll source 4U 1636−53
Z. S t u c h l ´ı k, M. U r b a n e c, A. K o t r l o v a´ ,
G. T o¨ r o¨ k and K. G o l u c h o v a´
Institute of Physics, Faculty of Philosophy and Science, Silesian University in Opava,
Bezruˇcovo nám. 13, CZ-74601 Opava, Czech Republic
e-mail: [email protected], [email protected]
ABSTRACT
The Resonant Switch (RS) model of twin high-frequency quasi-periodic oscillations (HF QPOs)
observed in neutron star binary systems, based on switch of the twin oscillations at a resonant
point, has been applied to the atoll source 4U 1636−53 under assumption that the neutron star
exterior can be approximated by the Kerr geometry. Strong restrictions of the neutron star parameters M (mass) and a (spin) arise due to fitting the frequency pairs admitted by the RS model
to the observed data in the regions related to the resonant points. The most precise variants of
the RS model are those combining the relativistic precession frequency relations with their modifications. Here, the neutron star mass and spin estimates given by the RS model are confronted
with a variety of equations of state (EoS) governing structure of neutron stars in the framework of
the Hartle–Thorne theory of rotating neutron stars applied for the observationally given rotation
frequency frot ∼ 580 Hz (or alternatively frot ∼ 290 Hz) of the neutron star at 4U 1636−53. It is
shown that only two variants of the RS model based on the Kerr approximation are compatible
with two EoS applied in the Hartle–Thorne theory for frot ∼ 580 Hz, while no variant of the RS
model is compatible for frot ∼ 290 Hz. The two compatible variants of the RS model are those
giving the best fits of the observational data. However, a self-consistency test by fitting the observational data to the RS model with oscillation frequencies governed by the Hartle–Thorne
geometry described by three spacetime parameters M, a and (quadrupole moment) q related by
the two available EoS puts strong restrictions. The test admits only one variant of the RS model
of twin HF QPOs for the Hartle–Thorne theory with the Gandolfi et al. (2010) EoS predicting
the parameters of the neutron star M ∼ 2.10 M⊙ , a ∼ 0.208, and q/a2 ∼ 1.77.
Keywords: Accretion, accretion disks — Stars: neutron — X-rays: binaries
1 Introduction
The high-frequency quasi-periodic oscillations (HF QPOs) in the Galactic Low Mass
X-Ray Binaries (LMXBs) containing neutron (quark) stars are often demonstrated as
two simultaneously observed pairs of peaks (twin peaks) in the Fourier power spectra corresponding to oscillations at the upper and lower frequencies (νU , νL ) that substantially change over time (even in one observational sequence). Most of the twin
1
SIMULATOR OF GALAXY MILLIMETER/SUBMILLIMETER EMISSION (SÍGAME): THE [Cii] −SFR
RELATIONSHIP OF MASSIVE Z=2 MAIN SEQUENCE GALAXIES
Karen P. Olsen1 , Thomas R. Greve2 , Desika Narayanan3 , Robert Thompson4 , Sune Toft1 , and Christian
Brinch5,6
ABSTRACT
´
We present SIGAME simulations of the [Cii] 157.7 µm fine structure line emission from cosmological
smoothed particle hydrodynamics (SPH) simulations of main sequence galaxies at z = 2. Using subgrid physics prescriptions the gas in our galaxy simulations is modelled as a multi-phased interstellar
medium (ISM) comprised of molecular gas residing in the inner regions of giant molecular clouds,
an atomic gas phase associated with photodissociation regions at the surface of the clouds, and a
diffuse, fully ionized gas phase. Adopting a density profile of the clouds and taking into account
heating by the local FUV radiation field and cosmic rays – both scaled by the local star formation
rate density – we calculate the [Cii] emission from each of the aforementioned ISM phases using a
large velocity gradient approach for each cloud, on resolved and global scales. The [Cii] emission
peaks in the central (<
∼ 1 kpc) regions of our galaxies where the star formation is most intense, and we
find that the majority (>
∼ 60%) of the emission in this region originates in the molecular gas phase. At
larger galactocentric distances (>
∼ 2 kpc), the atomic gas is the main contributor to the [Cii] emission
(>
∼ 80%), and at all radii the ionized gas provides a negligible amount (<
∼ 5%) to the [Cii] budget. Our
simulations predict a log-linear relationship between the integrated [Cii] luminosity and star formation
rate with a slope (0.80 ± 0.12) in agreement with observationally determined slopes (∼ 0.85 − 1.00)
but with a ∼ 3× higher normalization than the observed z ∼ 0 relation.
Subject headings: galaxies: high-redshift – galaxies: ISM – galaxies: star formation – ISM: lines and
bands
1. INTRODUCTION
Single ionized carbon (Cii) can be found throughout
the interstellar medium (ISM) of galaxies where gas is exposed to UV radiation with energies above the ionization
potential of neutral carbon (11.3 eV cf. 13.6 eV for hydrogen). Cii is found both in regions of ionized and neutral
gas where, depending on the gas phase, its fine structure
line [Cii] 2 P3/2 −2 P1/2 (λrest = 157.714 µm) is collisionally excited by electrons, Hi or H2 . The 2 P3/2 upper level
lies 91 K (= hν/kB ) above the 2 P1/2 ground state and,
over a large temperature range (∼ 20 − 8000 K), the critical density of [Cii] is only ∼ 5 − 44, ∼ 1600 − 3800 and
∼ 3300 − 7600 cm−3 for collisions with e− , Hi and H2 ,
respectively (Goldsmith et al. 2012). [Cii] is observed
to be one of the strongest cooling lines of the ISM, with
a line luminosity equivalent to ∼ 0.1 − 1% of the farinfrared (FIR) luminosity of galaxies (e.g., Stacey et al.
1991; Brauher et al. 2008; Casey et al. 2014).
[email protected]
1 Dark Cosmology Centre, Niels Bohr Institute, University of
Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark; [email protected]
2 Department of Physics and Astronomy, University College
London, Gower Street, London WC1E 6BT, UK
3 Department of Physics and Astronomy, Haverford College,
370 W Lancaster Ave., Haverford, PA 19041, USA
4 University of the Western Cape, 7535 Bellville, Cape Town,
South Africa
5 Centre for Star and Planet Formation (Starplan) and Niels
Bohr Institute, University of Copenhagen, Juliane Maries Vej
30, DK-2100 Copenhagen, Denmark
6 DeIC, Technical University of Denmark, Building 309, DK2800 Kgs. Lyngby, Denmark
Due to high atmospheric opacity at FIR wavelengths,
observations of [Cii] in the local Universe must be done
at high altitudes or in space. Indeed, the very first detections of [Cii] towards Galactic objects (Russell et al.
1980; Stacey et al. 1983; Kurtz et al. 1983) and other
galaxies (Crawford et al. 1985; Stacey et al. 1991; Madden et al. 1992) were done with airborne observatories
such as the NASA Lear Jet and the Kuiper Airborne
Observatory. The advent of the Infrared Space Observatory (ISO) allowed for the first systematic [Cii] surveys of
local galaxies (e.g., Malhotra et al. 1997; Luhman et al.
1998, 2003). Detections of [Cii] at high-z have also become feasible in recent years, with ground-based facilities (e.g., Maiolino et al. 2005, 2009; Hailey-Dunsheath
et al. 2010; Stacey et al. 2010) and the Herschel Space
Observatory (e.g., Gullberg et al. 2015). The Atacama
Large Millimeter Array (ALMA), owing to its tremendous collecting area and high angular resolution, is now
resolving [Cii] in high-z galaxies (De Breuck et al. 2014;
Wang et al. 2013) and pushing [Cii] observations of highz galaxies to much lower luminosity than before (Ouchi
et al. 2013; Maiolino et al. 2015; Capak et al. 2015).
In spite of the observational successes, the interpretation of the [Cii] line as a diagnostic of the ISM and
the star formation conditions in galaxies is complicated
by the fact that the [Cii] emission can originate from
different phases of the ISM. In our Galaxy, about 30 %
of the total [Cii] emission is found to come from dense
photo-dominated regions (PDRs), 25 % from cold Hi gas,
25 % from CO-dark H2 gas, and 20 % from ionized gas
(Pineda et al. 2014). We expect these percentages to
be different in other galaxies where high levels of star
Printed 3 July 2015
Fading Features Found in the Kinematics of the
Far-Reaching Milky Way Stellar Halo
Sarah
A. Bird1,2
1
⋆
and Chris Flynn3
Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences,
80 Nandan Road, Shanghai, 200030, China
2 Tuorla Observatory, Department of Physics and Astronomy, University of Turku, V¨
ais¨
al¨
antie 20, FI-21500 Kaarina, Finland
3 Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, VIC, 3122, Australia
Accepted 2015 June 26. Received 2015 June 25; in original form 2014 December 2
ABSTRACT
We test the long-term kinematical stability of a Galactic stellar halo model, due to
Kafle et al. (2012), who study the kinematics of approximately 5000 blue horizontal
branch (BHB) stars in the Sloan Digital Sky Survey (SDSS). The velocity dispersion σ
and anisotropy parameter β of the stars have been determined as functions of Galactocentric radius, over the range 6 < RGC < 25 kpc, and show a strong dip in the
anisotropy profile at RGC ∼ 17 kpc. By directly integrating orbits of particles in a
3-D model of the Galactic potential with these characteristics, we show that the σ
and β profiles quickly evolve on a time scale of a few × 10 Myr whereas the density ρ
profile remains largely unaffected. We suggest that the feature is therefore transient.
The origin of such features in the Galactic halo remains unclear.
Key words: galaxies: individual: Milky Way – Galaxy: halo – Galaxy: kinematics
and dynamics – stars: horizontal branch – stars: kinematics and dynamics.
1
INTRODUCTION
Studying the Milky Way’s stellar halo is an important route
to understanding galaxy formation, as the halo is such an
old Galactic component. Intrinsically bright stars with easily measured radial velocities have been the usual means of
doing so, with red giants and horizontal branch stars as typical tracers in such studies. Early studies of the stellar halo
kinematics date to the 1950s, and focused on halo stars passing through the Solar neighbourhood, but it was not until
the 1980s that large (& 100) samples of halo stars tens of
kpc from the Sun began to be collected and analysed (see
the reviews by Sandage (1986) and Helmi (2008)).
Milky Way halo BHB stars from ∼ 5 to 50 kpc
have been studied by Sommer-Larsen, Flynn & Christensen
(1994). They used about 100 stars to develop a kinematical model of the outer Milky Way halo, with the surprising result that the orbits of stars in the far outer halo
(> 20 kpc) appear to be much more tangential than radial. Flynn, Sommer-Larsen & Christensen (1996) used simulations of such stars orbiting in the Milky Way potential
which showed such a distribution of halo orbits is stable over
a Hubble time.
Since then, numerous studies have added to the sample
of BHB halo stars (Sommer-Larsen et al. 1997; Sirko et al.
⋆
2004; Deason, Belokurov & Evans 2011; Deason et al. 2012)
but show a wide spread in the resulting kinematical models
for the outer stellar halo.
Sommer-Larsen et al. (1997) analysed about 700 BHB
stars, mainly within 20 kpc of the Sun, but also probing out
to 50 kpc. They found that the outer stellar halo velocity
dispersion (at ≈ 50 kpc) was quite “cold” (i.e. low velocity
dispersion), nearing 100 km s−1 compared with the value
at the sun ≃ 140 km s−1 . They concluded that outer halo
orbits must be quite tangential (with a tangential velocity
dispersion of about 150 km s−1 ), given the observed density
distribution of halo stars and assumptions about the Milky
Way’s dark matter distribution.
On the other hand, Sirko et al. (2004) have advocated
an isothermal outer halo (RGC & R⊙ ), in which all three
components of the velocity dispersion are ≈ 100 km s−1 ,
based on ≈ 1200 BHB stars from SDSS. Thom et al. (2005)
subsequently analysed 530 BHB stars with radial velocities
and distances from the Hamburg/ESO survey, finding it difficult to discriminate between the simplest, isothermal kinematic models and anything more complex, and advocating
further studies of the inner halo to help resolve the issue.
Very distant BHB stars have recently been shown
by Deason, Belokurov & Evans (2011) and Deason et al.
(2012) to have very “cold” kinematics – low velocity dispersions of ≈ 50 − 60 km s−1 in the radial range 100 to
150 kpc. The density falloff in these regions is much steeper
Printed 3 July 2015
The formation history of massive cluster galaxies as
revealed by CARLA
E. A. Cooke1? , N. A. Hatch1 , A. Rettura2,3 , D. Wylezalek4 , A. Galametz5 ,
D. Stern2 , M. Brodwin6 , S. I. Muldrew7 , O. Almaini1 , C. J. Conselice1 ,
P.
R. Eisenhardt2 , W. G. Hartley8 , M. Jarvis9,10 , N. Seymour11 , S. A. Stanford12
1
School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
Propulsion Laboratory, California Institute of Technology, MS 169-234, Pasadena, CA 91109, USA
3 Infrared Processing and Analysis Center, California Institute of Technology, MS 220-6, Pasadena, CA 91125, USA
4 Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St, Baltimore, MD 21218, USA
5 Max-Planck-Institut fuer Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching, Germany
6 UMKC Department of Physics and Astronomy, 257 Flarsheim Hall, 5110 Rockhill Road, Kansas City, MO 64110, USA
7 Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
8 ETH Zurich, Institute for Astronomy, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
9 Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
10 Physics Department, University of the Western Cape, Bellville, South Africa
11 International Centre for Radio Astronomy Research, Curtin University, Perth, Australia
12 Physics Department, One Shields Avenue, University of California, Davis, CA 95616, USA
2 Jet
Accepted 2015 June 23. Received 2015 May 28; in original form 2015 March 17
ABSTRACT
We use a sample of 37 of the densest clusters and protoclusters across 1.3 6 z 6 3.2
from the Clusters Around Radio-Loud AGN (CARLA) survey to study the formation
of massive cluster galaxies. We use optical i0 -band and infrared 3.6 µm and 4.5 µm images to statistically select sources within these protoclusters and measure their median
observed colours; hi0 − [3.6]i. We find the abundance of massive galaxies within the
protoclusters increases with decreasing redshift, suggesting these objects may form an
evolutionary sequence, with the lower redshift clusters in the sample having similar
properties to the descendants of the high redshift protoclusters. We find that the protocluster galaxies have an approximately unevolving observed-frame i0 − [3.6] colour
across the examined redshift range. We compare the evolution of the hi0 − [3.6]i colour
of massive cluster galaxies with simplistic galaxy formation models. Taking the full
cluster population into account, we show that the formation of stars within the majority of massive cluster galaxies occurs over at least 2 Gyr, and peaks at z ∼ 2-3.
From the median i0 − [3.6] colours we cannot determine the star formation histories
of individual galaxies, but their star formation must have been rapidly terminated to
produce the observed red colours. Finally, we show that massive galaxies at z > 2
must have assembled within 0.5 Gyr of them forming a significant fraction of their
stars. This means that few massive galaxies in z > 2 protoclusters could have formed
via dry mergers.
Key words: galaxies: clusters: general ; galaxies: high-redshift ; galaxies: evolution
; galaxies: formation
1
INTRODUCTION
In the local Universe, most massive cluster galaxies are old
and have little-to-no ongoing star formation. They form
a very homogenous, slowly-evolving population, exhibit?
c 2015 RAS
ing similar, red colours. When viewed in colour-magnitude
space, these massive, old galaxies form a characteristic “red
sequence”. Such red sequences of galaxies are nearly ubiquitous in low redshift clusters, and persist out to z ∼ 1.5 (e.g.
Blakeslee et al. 2003; Holden et al. 2004; Mei et al. 2006;
Eisenhardt et al. 2008). Red sequences have commonly been
used to examine the formation history of massive cluster
Astronomy & Astrophysics manuscript no. 4u1636_final
July 3, 2015
c
ESO
2015
Long-term quasi-periodicity of 4U 1636–536 resulting from
accretion disc instability
Mateusz Wi´sniewicz1 , Agnieszka Słowikowska1 , Dorota Gondek-Rosińska1 , Andrzej A. Zdziarski2 , and
Agnieszka Janiuk3
1
2
July 3, 2015
ABSTRACT
We present the results of a study of the low-mass X-ray binary 4U 1636–536. We have performed temporal analysis of all available
RXTE/ASM, Swift/BAT and MAXI data. We have confirmed the previously discovered quasi-periodicity of ' 45 d present during
∼2004, however we found it continued to 2006. At other epochs, the quasi-periodicity is only transient, and the quasi-period, if present,
drifts. We have then applied a time-dependent accretion disc model to the interval with the significant X-ray quasi-periodicity. For our
best model, the period and the amplitude of the theoretical light curve agree well with that observed. The modelled quasi-periodicity
is due to the hydrogen thermal-ionization instability occurring in outer regions of the accretion disc. The model parameters are the
average mass accretion rate (estimated from the light curves), and the accretion disc viscosity parameters, α, for the hot and cold
phases. Our best model gives relatively low values of αcold ' 0.01 and αhot ' 0.03.
Key words. accretion, accretion discs – instabilities – stars: individual: (4U 1636–536, V801 Ara) – X-rays: binaries
1. Introduction
4U 1636–536 is a low-mass X-ray binary (LMXB) discovered
by Willmore et al. (1974). The photometry of the optical counterpart (V801 Ara) shows a short orbital period of 3.79 h (Giles
et al. 2002). The binary system consists of a late-type, lowmass (' 0.3–0.4 M ) donor, which transfers mass onto a neutron star (Fujimoto & Taam 1986; van Paradijs et al. 1990). Galloway et al. (2006) estimated the distance to 4U 1636–536 to
be D = 6.0 ± 0.5 kpc from Eddington limited X-ray bursts, assuming the neutron star mass of 1.4 M and the stellar radius
of 10 km. According to Casares et al. (2006), the mass function and mass ratio of 4U 1636–536 are f (M) = 0.76 ± 0.47 M
and M2 /MNS ' 0.21–0.34, respectively, where MNS is the mass
of the neutron star and M2 is the mass of the donor. They also
estimated the inclination as i ' 36◦ –60◦ . The binary is a persistent X-ray source, although it shows significant flux variations
on both long and short time scales. On time scales of hours, its
flux varies by a factor of ∼2–3 (Hoffman et al. 1977; Ohashi
et al. 1982; Breedon et al. 1986; Hasinger & van der Klis 1989).
The presence of kHz quasi-periodic oscillations, which are also
visible in the system during X-ray bursts, shows that the neutron star has been spun-up through accretion (Zhang et al. 1996;
Strohmayer 1999).
4U 1636–536 has been monitored daily in the 1.3–12.2 keV
energy range by the All Sky Monitor (ASM) on-board of the
Rossi X-ray Timing Explorer (RXTE) from 1996 until 2011. During the first four years of RXTE/ASM observations (1996–2000)
the source count rate was relatively stable at ∼ 15 cts s−1 . After
2000, it started to gradually decline and occasionally show a statistically significant quasi-periodic variability (Shih et al. 2005).
Those authors reported the presence of a long-period, ' 47 d,
1996
Rate (cts s−1 )
3
Institute of Astronomy, University of Zielona Góra, Szafrana 2, PL-65-516 Zielona Góra, Poland
Centrum Astronomiczne im. M. Kopernika, Bartycka 18, PL-00-716 Warszawa, Poland
Centre for Theoretical Physics, Polish Academy of Sciences, Al. Lotników 32/46, PL-02-668 Warsaw, Poland
1998
2000
2002
Year
2004
2006
2008
2010
2012
10
50000
51000
52000
53000
54000
MJD (days)
55000
56000
Fig. 1. The 50-d average RXTE/ASM light curve of 4U 1636–536 in the
energy range of 1.3–12.2 keV from January 1996 to November 2011.
quasi-periodic variability in the 2004 light curve. They suggested
that the observed flux variability is caused by the variability of
the accretion flow related to X-ray irradiation of the disc.
In our paper, we study the variability of 4U 1636–536 taking
into account the currently available data from three X-ray monitors, spanning almost 20 years (1996–2014). We interpret the
data in terms of a disc instability model. In Sect. 2, we describe
the X-ray data and perform their timing analysis. In Sect. 3, we
present the theoretical model of evolution of an accretion disc
around a neutron star used in the paper. We model the evolution
Mon. Not. R. Astron. Soc. 000, ??–23 (2014)
Printed 3 July 2015
Biases and systematics in the observational derivation of
galaxy properties: comparing different techniques on
synthetic observations of simulated galaxies.
Giovanni
Guidi1, Cecilia Scannapieco1 and C. Jakob Walcher1
1
Leibniz-Institut f¨
ur Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482, Potsdam, Germany
Accepted 3 July 2015 Received ...; in original form ...
ABSTRACT
We study the sources of biases and systematics in the derivation of galaxy properties
of observational studies, focusing on stellar masses, star formation rates, gas/stellar
metallicities, stellar ages and magnitudes/colors. We use hydrodynamical cosmological simulations of galaxy formation, for which the real quantities are known, and
apply observational techniques to derive the observables. We also make an analysis
of biases that are relevant for a proper comparison between simulations and observations. For our study, we post-process the simulation outputs to calculate the galaxies’
spectral energy distributions (SEDs) using Stellar Population Synthesis models and
also generating the fully-consistent far UV-submillimeter wavelength SEDs with the
radiative transfer code sunrise. We compared the direct results of simulations with
the observationally-derived quantities obtained in various ways, and found that systematic differences in all studied galaxy properties appear, which are caused by: (1)
purely observational biases (e.g. fiber size for single-fiber spectroscopic surveys), (2)
the use of mass-weighted/luminosity-weighted quantities, with preferential sampling
of more massive/luminous regions, (3) the different ways to construct the template
of models when a fit to the spectra is performed, and (4) variations due to the use
of different calibrations, most notably in the cases of the gas metallicities and star
formation rates. Our results show that large differences, in some cases of more than
an order of magnitude, can appear depending on the technique used to derive galaxy
properties. Understanding these differences is of primary importance both for simulators, to allow a better judgement on similarities/differences with observations, and for
observers, to allow a proper interpretation of the data which inevitably suffers from
observational biases which vary from survey to survey.
Key words: galaxies: formation - evolution - cosmology: theory - methods: SPH
simulations - SPS models - radiative transfer
1
INTRODUCTION
In recent years, large galaxy surveys such as the 2dFGRS
(Two-degree-field Galaxy Redshift Survey, Colless 1999),
SDSS (Sloan Digital Sky Survey, Abazajian et al. 2003) and
2MASS (Two Micron All-Sky Survey, Skrutskie et al. 2006),
have opened up the possibility to statistically study the
properties of galaxies in the Local Universe, revealing their
great diversity: even for a narrow range in stellar mass,
galaxies appear in a large variety of morphologies, gas fractions, star formation rates (SFRs) and chemical abundances.
These observations have also allowed to identify important
relations such as the mass-metallicity (Garnett & Shields
1987; Tremonti et al. 2004), and to measure the corresponding scatter which encodes relevant information on the galaxies’ evolution. These wealth of data give important insight
c 2014 RAS
on the process of galaxy formation and evolution, revealing the action of physical mechanisms occurring in galaxies,
both internal – e.g. feedback, cooling – and in relation to
larger-scale mechanisms – mergers, interactions, accretion.
All these leave imprints on the shape of the spectral energy
distributions (SEDs) which constitute the primary source of
information of large galaxy surveys. In fact, in recent years it
became possible to obtain the full SEDs of galaxies at wavelengths from the X-Ray to the radio. In particular for galaxy
studies, wavelengths from the ultraviolet to the far infrared
are the most relevant as they directly trace the spectrum
coming from the stars and interstellar gas/dust, and are not
affected by other processes (such as shocks, accretion onto
compact objects, etc), unrelated to the stellar light.
In addition to observations, numerical simulations
Printed 3 July 2015
Supernova-Driven Outflows in NGC 7552: A Comparison of H α
and UV Tracers
Corey M. Wood,1? Christy A. Tremonti,1 Daniela Calzetti,2 Claus Leitherer,3
John
Chisholm,1 and John S. Gallagher III1
1
Department of Astronomy, University of Wisconsin–Madison, 475 N. Charter St., Madison, WI 53706, USA
of Astronomy, University of Massachusetts, Amherst, MA 01003, USA
3 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
2 Department
3 July 2015
ABSTRACT
We investigate the supernova-driven galactic wind of the barred spiral galaxy NGC 7552,
using both ground-based optical nebular emission lines and far-ultraviolet absorption lines
measured with the Hubble Space Telescope Cosmic Origins Spectrograph. We detect broad
(∼ 300 km s−1 ) blueshifted (−40 km s−1 ) optical emission lines associated with the galaxy’s
kpc-scale star-forming ring. The broad line kinematics and diagnostic line ratios suggest that
the H α emission comes from clouds of high density gas entrained in a turbulent outflow.
We compare the H α emission line profile to the UV absorption line profile measured along
a coincident sight line and find significant differences. The maximum blueshift of the H αemitting gas is ∼ 290 km s−1 , whereas the UV line profile extends to blueshifts upwards of
1000 km s−1 . The mass outflow rate estimated from the UV is roughly nine times greater
than that estimated from H α. We argue that the H α emission traces a cluster-scale outflow of
dense, low velocity gas at the base of the large-scale wind. We suggest that UV absorption line
measurements are therefore more reliable tracers of warm gas in starburst-driven outflows.
Key words: galaxies: starburst – galaxies: individual: NGC 7552 – galaxies: evolution –
ISM: jets and outflows
1
INTRODUCTION
Feedback from massive stellar winds and supernova explosions has
long been identified as a mechanism capable of injecting large
amounts of energy into the local interstellar medium (ISM) of a
galaxy, resulting in both the heating and potential removal of the
gas in the form of a wind (Larson 1974). Supernovae-driven winds
have myriad profound effects on galaxy evolution, influencing the
shape of the galaxy luminosity function (Benson et al. 2003), the
mass-metallicity relation (Finlator & Davé 2008), and the structure of galactic disks (Scannapieco et al. 2008). Such winds have
been found to be “ubiquitous” in star-forming galaxies where star
formation surface densities exceed ΣSF R ≈ 0.1 M yr−1 kpc−2
(Heckman 2002). Under these conditions, rapid star formation results in a large injection of mechanical energy into the local ISM of
the galaxy by OB stars, Wolf-Rayet stars, and supernovae.
Although galactic winds are commonly observed both locally
and, increasingly, in the high-redshift universe (e.g., Veilleux et al.
2005; Steidel et al. 2010), it has been difficult to determine how
much mass these winds remove from their host galaxies. The extent to which galactic winds affect on-going star formation de-
?
c 2015 RAS
pends highly on the ability of such winds to remove gas from
their hosts, commonly parameterized as the mass loading factor
η = M˙ out /M˙ ∗ , the rate of mass loss due to an outflow as a fraction
of the global star formation rate. Measured mass loading factors
are typically around η ∼ 1, but many of these measurements come
with high uncertainties. Rupke et al. (2005) measure mass loading
factors of η ≈ 0.01 – 1 in ∼ 45 starburst-dominated galaxies at
z < 0.5. These measurements suffer from order-of-magnitude uncertainties due to large ionization corrections for Na I absorption
lines. Bouché et al. (2012) measure η ∼ 2 with uncertainties of
only a factor of 2 for five galaxies studied via background quasar
absorption, but warn that it may be incorrect to compare outflows
measured at large impact parameter to the current level of star formation. At higher redshift, Pettini et al. (2002) estimate η ∼ 1 in
a single Lyman break galaxy at z = 2.73. Newman et al. (2012b)
measure η ∼ 2 for high-ΣSF R systems at z ∼ 2, but these measurements suffer from quoted uncertainties of at least a factor of 3.
The uncertainties are possibly much larger due to uncertainties in
the electron density measurement because of low-S/N in the [S II]
lines. More robust measurements of outflow masses and velocities
will provide better constraints on mass loading factors.
Mass loss measurements have typically been easier to perform in absorption-line studies, where the column density of the
Mon. Not. R. Astron. Soc. 000, 1–15 (yyyy)
Printed 3 July 2015
Predicted multiply-imaged X-ray AGNs in the XXL survey
F. Finet1,2⋆, A. Elyiv2,3,4, O. Melnyk2,5, O. Wertz2, C. Horellou6, J. Surdej2†
1 Aryabhatta
Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital-263 129, Uttarakhand (India)
Astrophysics and Space Observations (AEOS), University of Li`
ege,
All´
ee du 6 Aoˆ
ut, 17 (Sart Tilman, Bˆ
at. B5c), 4000 Li`
ege, Belgium
3 Main Astronomical Observatory, Academy of Sciences of Ukraine, 27 Akademika Zabolotnoho St., 03680 Kyiv, Ukraine
4 Dipartimento di Fisica e Astronomia, Universit`
a di Bologna, Viale Berti Pichat 6/2, I-40127 Bologna, Italy
5 Astronomical Observatory, Kyiv National University, 3 Observatorna St., 04053 Kyiv, Ukraine
6 Dept.of Earth & Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala, Sweden
2 Extragalactic
Accepted yyyy Month dd. Received yyyy Month dd; in original form yyyy Month dd
ABSTRACT
We estimate the incidence of multiply-imaged AGNs among the optical counterparts
of X-ray selected point-like sources in the XXL field. We also derive the expected
statistical properties of this sample, such as the redshift distribution of the lensed
sources and of the deflectors that lead to the formation of multiple images, modelling
the deflectors using both spherical (SIS) and ellipsoidal (SIE) singular isothermal mass
distributions. We further assume that the XXL survey sample has the same overall
properties as the smaller XMM-COSMOS sample restricted to the same flux limits
and taking into account the detection probability of the XXL survey.
Among the X-ray sources with a flux in the [0.5 − 2] keV band larger than 3.0 ×
10−15 erg cm−2 s−1 and with optical counterparts brighter than an r-band magnitude
of 25, we expect ∼ 20 multiply-imaged sources. Out of these, ∼16 should be detected
if the search is made among the seeing-limited images of the X-ray AGN optical
counterparts and only one of them should be composed of more than two lensed images.
Finally, we study the impact of the cosmological model on the expected fraction of
lensed sources.
Key words: Gravitational lensing statistics– AGNs – XXL survey – XMM-Newton
1
INTRODUCTION
1
The XXL survey , carried out by the space-based X-ray observatory XMM-Newton, spans over ∼ 2 × 25 square degrees with near 10 ks exposure in each field and is expected
to lead to the detection of ∼ 25000 Active Galactic Nuclei (AGNs) down to a limiting flux 10−15 erg cm−2 s−1
in the [0.5 − 2] keV soft X-ray band (Pierre et al. 2015).
These X-ray data are complemented by multi-wavelength
data obtained with the Canada-France-Hawaii Telescope
Legacy Survey (CFHTLS) and with the Blanco telescope
(Blanco/South Pole Telescope (SPT) Cosmology Survey,
BCS) in the (near-)optical u’, g, r, i and z bands, down
to a limiting AB magnitude of ∼ 25. Beside the multi-band
imaging of the XXL fields, there is a very large on-going effort to obtain optical spectra of XXL sources, through either
the matching of existing survey catalogues or dedicated spectroscopic surveys. Among these spectroscopic data acquisition programmes, the VIMOS Public Extragalactic Redshift
⋆
E-mail:[email protected]
† Also, Directeur de Recherche honoraire du F.R.S.-FNRS
1 http://ifru.cea.fr/xxl
Survey (VIPERS, A.Guzzo & Le Fèvre 2010) covers most
of the northern field, the southern field being covered using the AAOmega multi-object spectrograph on the AngloAustralian Telescope, an instrument used for the Galaxy and
mass assembly project (GAMA, Driver et al. 2009).
The completeness of this multi-wavelength database
over the entire XXL field provides a unique sample to search
for multiply-imaged AGNs. We have thus initiated such a
search among the optical counterparts of point-like sources
in the soft X-ray band. Beside the scientific interest provided
by each multiply-imaged source, the goal of this project is
to construct a statistically clean sample of lensed sources
that will be used, in combination with samples of multiplyimaged sources from other recent surveys, to independently
constrain the cosmological model.
The choice of the soft X-ray point-like sources is motivated by the higher sensitivity of XMM-Newton in this band.
Furthermore, this spectral band should contain a larger fraction of type-I AGNs than the hard X-ray. On average, type-I
AGNs with a detectable optical counterpart are expected to
have a higher redshift than type-II AGNs (more absorbed
in the visible and thus more difficult to detect in the optical
TURBULENT AMPLIFICATION AND STRUCTURE OF INTRACLUSTER MAGNETIC FIELD
Andrey Beresnyak
Nordita, KTH Royal Institute of Technology and Stockholm University, SE-10691 Stockholm, Sweden
Francesco Miniati
Physics Dept., ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Switzerland
ABSTRACT
We compare DNS calculations of homogeneous isotropic turbulence with the statistical properties
of intra-cluster turbulence from the Matryoshka Run (Miniati 2014) and find remarkable similarities
between their inertial ranges. This allowed us to use the time dependent statistical properties of intracluster turbulence to evaluate dynamo action in the intra-cluster medium, based on earlier results from
numerically resolved nonlinear magneto-hydrodynamic turbulent dynamo (Beresnyak 2012). We argue
that this approach is necessary (a) to properly normalize dynamo action to the available intra-cluster
turbulent energy and (b) to overcome the limitations of low Re affecting current numerical models
of the intra-cluster medium. We find that while the properties of intra-cluster magnetic field are
largely insensitive to the value and origin of the seed field, the resulting values for the Alfvén speed
and the outer scale of the magnetic field are consistent with current observational estimates, basically
confirming the idea that magnetic field in today’s galaxy clusters is a record of its past turbulent
activity.
Subject headings: cosmology: theory—magnetohydrodynamics—MHD dynamo
1. INTRODUCTION
The hot intracluster medium (ICM) of galaxy clusters
(GC) is well known to be magnetized from radio observations. These reveal both the occurrence of Faraday
rotation effect on polarized radiation from background
quasars (Clarke et al. 2001; Clarke 2004) and of diffuse
synchrotron emission (Ferrari et al. 2008) from the ICM.
Estimates of the magnetic field based on these observations range between a fraction and several µG. Measurements on the structural and spectral features are sparse
and more difficult, but indicate steep power-laws below few tens of kpc (Laing et al. 2008; Kuchar & Enßlin
2011). For massive clusters, turbulence in the ICM is
mainly driven by structure formation (Norman & Bryan
1999; Ryu et al. 2008; Vazza et al. 2011; Miniati 2014,
2015). The most important magnetic field amplification mechanism in the ICM is the small scale or fluctuation dynamo (SSD), operating on scales smaller than
the turbulence outer scale. Kinematic regime of SSD,
i.e. when the back reaction of the magnetic field on the
flow is negligible, has been studied in great detail previously (Kazantsev 1968; Kraichnan & Nagarajan 1967;
Kulsrud & Anderson 1992). In kinematic regime the
magnetic energy grows exponentially, till the approximation breaks down, roughly in a dynamical time multiplied by Re−1/2 , where Re is an effective Reynolds number. The extremely hot and rarefied plasma of the cluster
have very large collisional mean free paths, around
λ ≈ 103 pc(n/3 × 10−3 cm−3 )−1 (T /10keV)3/2 ,
(1)
at the same time, given the observable magnetic fields
around 3 µG, the Larmor radius is smaller by many orders of magnitudes:
rL ≈ 10−9 pc(T /10keV)(B/3µG)−1 .
(2)
Such situation, known as “collisionless plasma” is
challenging from theoretical viewpoint, since nonlinear
plasma effects are dominating the transport, which has
been known since early Lab plasma experiments, when
it became clear that collisional “classic transport” is
grossly insufficient to explain cross field diffusion (see,
e.g., Galeev & Sagdeev 1979). As a rule of thumb,
the actual effective parallel mean free path is smaller
than the one obtained by collisional formula, but larger
than the Bohm estimate (λef f ∼ rL ). The search for
this “mesoscale” for cluster conditions resulted in estimates for the mean free path of the proton in the ICM
around 10−3 − 10−6 pc (Schekochihin & Cowley 2006;
Beresnyak & Lazarian 2006; Schekochihin et al. 2008;
Brunetti & Lazarian 2011). From these estimates we expect clusters to be turbulent with Reynolds numbers Re
exceeding 1012 . Combining this with the above estimate
of the kinematic SSD growth rates, for a dynamical time
∼ eddy turnover time ∼ 1 Gyr (Miniati 2014), we estimate that the exponentiation timescale will be smaller
than 1 Gyr (Re)−1/2 ≈ 1 kyr.
The remainder of this paper is organized as follows: in
Section 2 we discuss the properties of nonlinear regime
of the small-scale dynamo which is supposed to dominate during most of the cluster lifetime; in Section 3 we
point to the inadequacy of current MHD cosmological
simulations, as far as dynamo is concerned, and suggest
a different approach; in Section 4 we describe new homogeneous dynamo simulations with intermittent driving;
in Section 5 we explain our cosmological hydrodynamic
model of the cluster; in Section 6 we combine the knowledge obtained in previous sections and analyze cluster
simulations to derive the properties of the cluster magnetic fields; in Section 7 we discuss implications and compare with previous work.
Astronomy & Astrophysics manuscript no. censors_peak_paper_aa_rv
July 3, 2015
c
ESO
2015
Cosmic downsizing of powerful radio galaxies to low radio
luminosities
(Research Note)
E. E. Rigby1 , J. Argyle1, 2 , P. N. Best3 , D. Rosario4 and H. J. A. Röttgering1
1
2
3
4
Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands
School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, KY16 9SS, UK
SUPA, Institute for Astronomy, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse 1, 85748 Garching, Germany
July 3, 2015
ABSTRACT
Aims. At bright radio powers (P1.4GHz > 1025 W/Hz) the space density of the most powerful sources peaks at higher redshift than
that of their weaker counterparts. This paper establishes whether this luminosity–dependent evolution persists for sources an order of
magnitude fainter than those previously studied, by measuring the steep–spectrum radio luminosity function (RLF) across the range
1024 < P1.4GHz < 1028 W/Hz, out to high redshift.
Methods. A grid–based modelling method is used, in which no assumptions are made about the RLF shape and high–redshift behaviour. The inputs to the model are the same as in Rigby et al. (2011): redshift distributions from radio source samples, together
with source counts and determinations of the local luminosity function. However, to improve coverage of the radio power vs. redshift
plane at the lowest radio powers, a new faint radio sample is introduced. This covers 0.8 sq. deg., in the Subaru/XMM–Newton Deep
Field, to a 1.4 GHz flux density limit of S 1.4GHz ≥ 100 µJy, with 99% redshift completeness.
Results. The modelling results show that the previously seen high–redshift declines in space density persist to P1.4GHz < 1025 W/Hz.
At P1.4GHz > 1026 W/Hz the redshift of the peak space density increases with luminosity, whilst at lower radio luminosities the position
of the peak remains constant within the uncertainties. This ‘cosmic downsizing’ behaviour is found to be similar to that seen at optical
wavelengths for quasars, and is interpreted as representing the transition from radiatively efficient to inefficient accretion modes in the
steep–spectrum population. This conclusion is supported by constructing simple models for the space density evolution of these two
different radio galaxy classes; these are able to successfully reproduce the observed variation in peak redshift.
Key words. galaxies: active – galaxies: evolution – galaxies: high redshift
1. Introduction
Radio–loud active galactic nuclei are a key component driving
galaxy evolution; the feedback their expanding radio jets provide is essential for preventing large–scale cluster cooling flows
and halting the growth of massive elliptical galaxies (e.g. Fabian
et al. 2006; Best et al. 2006; Best et al. 2007; Croton et al. 2006;
Bower et al. 2006). To understand the timescales upon which
these processes occur, it is important to first understand the evolution of the radio luminosity function (RLF) to high–redshift.
An early measurement of this came from Dunlop & Peacock
(1990), who found increases in the space density of both flat
and steep–spectrum radio AGN of two to three orders of magnitude, over that seen locally. They also saw the first indication
of an expected higher redshift density decline at z ∼ 2.5, corresponding to the build–up of these objects in the early Universe.
However, their work, and that of subsequent studies (e.g. Shaver
et al. 1996; Jarvis et al. 2001; Waddington et al. 2001), lacked the
necessary depth and volume needed to unambiguously measure
this high–redshift behaviour.
This situation improved with the development of the Combined EIS–NVSS Survey of Radio Sources (CENSORS; Best et
al. 2003): a survey designed to maximise the coverage of steep–
spectrum radio sources close to the high–redshift break in the
RLF. Rigby et al. (2011, hereafter R11) used CENSORS, combined with additional radio source samples, source counts and
determinations of the local RLF, to investigate the space density evolution of the P1.4GHz > 1025 W/Hz steep–spectrum population via grid–based modelling with no prior assumptions included about the high–redshift behaviour. This robustly identified the post–peak space density decline in the RLF, and found
that this turnover appears to be luminosity–dependent; at lower
radio powers (P1.4GHz = 1025−26 W/Hz) the space densities peak
at z >
∼ 1, but the peak moves to higher redshift for the more lu27
minous objects (z >
∼ 3 for P1.4GHz > 10 W/Hz). A luminosity
dependence in the position of the steep–spectrum RLF peak can
be interpreted as a sign of ‘cosmic downsizing’, in which the
most massive black holes form at earlier epochs than their less
massive counterparts. This has also been seen for other AGN
populations, selected at other radio, optical, far–infrared and X–
ray wavelengths (e.g. De Zotti et al. 2010; Hasinger et al. 2005;
Richards et al. 2005; McAlpine et al. 2013; Delvecchio et al.
2014), as well as reproduced in simulations of black hole growth
(e.g. Fanidakis et al. 2012; Hirschmann et al. 2012, 2014).
Steep–spectrum radio sources can be split into two distinct
populations: typically powerful objects with ‘standard’ accretion
of cold gas and likely to be merger driven (‘cold–mode’); and
ON THE [CII]-SFR RELATION IN HIGH REDSHIFT GALAXIES
L. Vallini1
Dipartimento di Fisica e Astronomia, Universit´
a di Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy
S. Gallerani, A. Ferrara2 , A. Pallottini, B. Yue
Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126, Pisa, Italy
ABSTRACT
After two ALMA observing cycles, only a handful of [C II] 158 µm emission line searches in z > 6
galaxies have reported a positive detection, questioning the applicability of the local [C II]-SFR relation
to high-z systems. To investigate this issue we use the Vallini et al. (2013, V13) model, based
on high-resolution, radiative transfer cosmological simulations to predict the [C II] emission from
the interstellar medium of a z ≈ 7 (halo mass Mh = 1.17 × 1011 M ) galaxy. We improve the
V13 model by including (a) a physically-motivated metallicity (Z) distribution of the gas, (b) the
contribution of Photo-Dissociation Regions (PDRs), (c) the effects of Cosmic Microwave Background
on the [C II] line luminosity. We study the relative contribution of diffuse neutral gas to the total
[C II] emission (Fdiff /Ftot ) for different SFR and Z values. We find that the [C II] emission arises
predominantly from PDRs: regardless of the galaxy properties, Fdiff /Ftot ≤ 10% since, at these early
epochs, the CMB temperature approaches the spin temperature of the [C II] transition in the cold
neutral medium (TCMB ∼ TsCNM ∼ 20 K). Our model predicts a high-z [C II]-SFR relation consistent
with observations of local dwarf galaxies (0.02 < Z/Z < 0.5). The [C II] deficit suggested by actual
data (LCII < 2.0 × 107 L in BDF3299 at z ≈ 7.1) if confirmed by deeper ALMA observations,
can be ascribed to negative stellar feedback disrupting molecular clouds around star formation sites.
The deviation from the local [C II]-SFR would then imply a modified Kennicutt-Schmidt relation in
z > 6 galaxies. Alternatively/in addition, the deficit might be explained by low gas metallicities
(Z < 0.1 Z ).
Subject headings: galaxies:high-redshift, galaxies:ism, cosmology:theory, submillimeter:ism,
line:formation, cosmology:observations
1. INTRODUCTION
The study and characterization of the interstellar
medium (ISM) of galaxies that formed in the early Universe is entering a golden era thanks to the unprecedented capabilities of the Atacama Large Millimetersubmillimeter Array (ALMA). In particular, the 158 µm
emission line due to the 2 P3/2 →2 P1/2 fine-structure
transition of ionized carbon ([C II]), being the dominant
coolant of the neutral diffuse ISM (Wolfire et al. 2003), is
by far the brightest line in the far-infrared band (Stacey
et al. 1991). In addition to the diffuse neutral gas, the
[C II] line can be excited in other components of the interstellar medium such as high density photodissociation
regions (PDRs), and in the diffuse ionized gas, where
the main driver of the [C II] emissivity are the collisions
with free e− . Although precisely assessing the relative
contribution of the various gas phases to the total line
emission might be difficult, [C II] line remains a unique
tool to characterize the interstellar medium of galaxies in the Epoch of Reionization (z ∼ 6) (e.g Carilli
& Walter 2013). Before the ALMA advent, the [C II]
line from z > 4 was solely detected in galaxies with extreme star formation rates (≈1000 M yr−1 ) (e.g. Cox
1
2
Scuola Normale Superiore, Pisa, Italy
Kavli IPMU (WPI), Todai Institutes for Advanced Study,
the University of Tokyo
et al. 2011; Carilli et al. 2013; Carniani et al. 2013; De
Breuck et al. 2014), or in those hosting Active Galactic Nuclei (AGN) (e.g. Maiolino et al. 2005; Venemans
et al. 2012; Gallerani et al. 2012; Cicone et al. 2015). In
the first years of ALMA operations, the [C II] has been
detected in a handful of galaxies at z ≈ 4.5 with modest star formation rates (50 − 300 M yr−1 ) (Carilli et al.
2013; Carniani et al. 2013; Williams et al. 2014; Riechers
et al. 2014). Viceversa, other tentative searches of this
line have failed in normal star-forming galaxies (NSFGs;
SFR ≈10 M yr−1 ) at z > 6 (e.g. Walter et al. 2012;
Kanekar et al. 2013; González-López et al. 2014; Ouchi
et al. 2013; Ota et al. 2014; Schaerer et al. 2015). These
early results seem to be at odds with the correlation between the intensity of the [C II] line and the SFR found
in local galaxies, thus questioning the applicability of
this relation to high-z sources. Only very recently, three
different ALMA campaigns targeting z ≈ 5 − 7 LAEs
and LBGs have yielded [C II] detections: Maiolino et al.
(2015) in the vicinity of BDF3299, a LAE at z ≈ 7.1, Capak et al. (2015) in a sample of LAEs at 5.1 < z < 5.7,
and Willott et al. (2015) in two luminous LBGs at z ≈ 6
being in agreement with the [C II] luminosity expected
from lower-z observations in star forming galaxies.
In the nearby Universe, the [C II]-SFR relation holds
for a wide range of galaxy types, ranging from metal
poor dwarf galaxies, to starbursts, ultra-luminous in-

Cosmological dynamics with non-minimally coupled scalar field and

Transcription

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