The Pan-Andromeda Archaeological Survey

The Pan-Andromeda Archaeological Survey

PAndAS mining the stellar
halo of Andromeda
Stellar streams, dwarf galaxies, globular clusters et al.
Nicolas Martin
(Strasbourg Observatory &
Max Planck Institute for Astronomy)
PAndAS team
(PI: Alan McConnachie)
Cosmology on galaxy scales
the new frontier
๏ Large
scale cosmology is
now largely understood
•
Λ Cold Dark Matter universe
๏ How
do baryons condense
at the center of dark matter
halos?
•
hierarchical build-up (stars,
globular clusters, gas…)
Aquarius simulation, Springel et al. (2009)
Cosmology on galaxy scales
the new frontier
“observed” halo
kpc
๏ Large
scale cosmology is
now largely understood
•
Λ Cold Dark Matter universe
๏ How
do baryons condense
at the center of dark matter
halos?
•
hierarchical build-up (stars,
globular clusters, gas…)
Cooper et al. (2009)
see also Kathryn’s talk
Why study the faintest galaxies?
๏ Massive
galaxies contain the
majority of the universe’s stellar
mass
๏ Is
•
•
sensitive to star-formationsuppression mechanisms
“missing satellite crisis”?
500 kpc
there a faint end to galaxy
formation?
๏ Which
dark matter halos
contain stars?
•
What sets their numbers? their
properties (luminosity, size,
shape)?
Springel et al. (2009)
M31
PAndAS
The Panoramic Andromeda Archaeological Survey
PI: Alan McConnachie
Arif Babul, Mike Barker, Pauline Barmby, Edouard Bernard, Crystal Brasseur, Scott Chapman, Robert Cockcroft, Michelle
Collins, Anthony Conn, Pat Côté, Tim Davidge, Anjali Doney, Aaron Dotter, John Dubinski, Greg Fahlman, Mark Fardal,
Annette Ferguson, Jurgen Fliri, Bill Harris, Avon Huxor, Rodrigo Ibata, Mike Irwin, Geraint Lewis, Dougal Mackey, Nicolas
Martin, Mustapha Moucine, Julio Navarro, Jorge Peñarrubia, Thomas Puzia, Mike Rich, Jenny Richardson, Harvey Richer,
Arnaud Siebert, Nial Tanvir, David Valls-Gabaud, Kim Venn, Larry Widrow, Kristin Woodley...
PAndAS
The Pan-Andromeda Archaeological Survey (2008–2011)
๏ Building
on pilot M31 CFHT
surveys (Ibata, Martin et al. 2007,
McConnachie et al. 2008)
๏ CFHT
large program
•
220 hours over 3 years
•
3.6m telescope on Mauna Kea
๏ MegaCam/MegaPrime
•
1 deg2 field of view
•
2 bands (g & i)
๏ All
~400 deg2 now observed
tip of RGB
3 mag. below the
•
0.5–0.8” seeing
•
~20 min integration in g & i
•
S/N=10 depths
•
g ≈ 25.5
•
i ≈ 24.5
๏ 96
million sources
๏ ~10
million stars in M31
RGB selection box
Galactic disk
๏ Observing
Galactic halo
PAndAS data
Stellar halo of M31
Different stellar populations
→age/metallicity/distance differences
Let us assume metallicity differences…
150 kpc
[Fe/H] = –2.3
–2.1
–1.9
–1.7
–1.5
–1.3
–1.1
–0.9
–0.7
@ M31 distance
50 kpc
Measuring Shape/Lumpiness of the halo
• Ibata et al. (2012)
• McConnachie et al. (2012/13)
150 kpc
12
A.P. Cooper et al.
Volume explored
around MW by SDSS
kpc
50 kpc
Cooper et al. (2010)
Star/HI comparison
PAndAS in the mist
3
Lewis, Braun et al. (2012)
-346
-290
-383
-300
-300
-247
-417
-240
-180
-280
Metal-poor
M31 RGBs
HI gas
The M31 satellite systems
PAndAS’ Cubs: Dwarf galaxies & globular clusters
Cas II
Zucker et al. (2004; 1)
Martin et al. (2006; 3)
Ibata, Martin et al. (2007; 2)
Irwin et al. (2007; 1)
Zucker et al. (2007; 1)
McConnachie et al. (2008; 3)
Martin et al. (2009; 2)
Richardson et al. (2011, 5)
Bell, Slater & Martin (2011, 1)
Slater, Bell & Martin (2011, 1)
Irwin et al. (in prep, 1)
Tri I
6 dSphs (2004) → 28 dSphs (now;
4 SDSS + 16 PAndAS)
+ deep follow-up
Two examples
760
MARTIN ET AL.
Vol. 705
Martin et al. (2009)
i
And XXI
MV = –9.9±0.6
rh = 875±127 pc
Figure 2. Left panel: spatial distribution of stellar sources around And XXI. Small dots represent all stars in the PAndAS survey whereas large dots correspond to
likely RGB stars of the dwarf galaxy, selected within the dashed box shown on the CMD of the middle panel. These stars are clearly clumped into an overdensity of
stars. MegaCam CCDs are shown as dashed rectangles and white regions correspond to holes in-between CCDs or holes in the survey. Open circles correspond to
regions that are lost to the survey due to the presence of saturated bright stars. The central dashed ellipse corresponds to the region within two half-light radii of the
dwarf galaxy, assuming the structural parameters listed in Table 1. Right panels: color–magnitude diagrams within two half-light radii of And XXI (middle panel)
and, for comparison, of a field region at a distance of ∼20" covering the same area after correcting from gaps in the survey coverage (rightmost panel). The galaxy’s
RGB is clearly visible as an overdensity of stars with 0.8 ! g − i ! 1.5 and i " 21.2 that does not appear in the reference CMD.
(A color version of this figure is available in the online journal.)
Y
X
g-i
Figure 2. Left panel: spatial distribution of stellar sources around And XXI. Small dots represent all stars in the PAndAS survey whereas large dots correspond to
likely RGB stars of the dwarf galaxy, selected within the dashed box shown on the CMD of the middle panel. These stars are clearly clumped into an overdensity of
stars. MegaCam CCDs are shown as dashed rectangles and white regions correspond to holes in-between CCDs or holes in the survey. Open circles correspond to
regions that are lost to the survey due to the presence of saturated bright stars. The central dashed ellipse corresponds to the region within two half-light radii of the
dwarf galaxy, assuming the structural parameters listed in Table 1. Right panels: color–magnitude diagrams within two half-light radii of And XXI (middle panel)
and, for comparison, of a field region at a distance of ∼20" covering the same area after correcting from gaps in the survey coverage (rightmost panel). The galaxy’s
RGB is clearly visible as an overdensity of stars with 0.8 ! g − i ! 1.5 and i " 21.2 that does not appear in the reference CMD.
(A color version of this figure is available in the online journal.)
And XXII
MV = –6.5±0.8
rh ~ 220 pc
Figure 3. Same as Figure 2 but for And XXII. Although this system is much fainter, it still appears as a spatial overdensity of stars (left panel) that are aligned along a
RGB in the CMD (middle panel), a feature that does not appear in the reference CMD (right panel).
Bayesian TRGB distance analysis
A. Conn et al. (2011, 2012)
And I
Bayesian TRGB distance analysis
A. Conn et al. (2011, 2012)
550
kpc
950 300
900 300
1000
Bayesian distance analysis
A. Conn et al. (2011, 2012)
Homogeneous
c)
distances
Automatic search & completeness limits
Martin et al. (2012)
๏ Full
statistical analysis of
spatial + CMD information
•
Accounting for varying MW
foreground contamination,
very structured M31
“contamination”
Automatic search & completeness limits
Martin et al. (2012)
๏ Full
•
Accounting for varying MW
foreground contamination,
very structured M31
“contamination”
๏ Automated
•
•
XI
search:
completeness function as
f(X,Y,rh,[Fe/H],m-M,…)
new candidate dwarf
galaxies
→
XII
comparison with simulations
XIII
M06 GC
detection S/N
statistical analysis of
spatial + CMD information
Dwarf galaxy radial velocities
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a ters!
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Collins et al. (2011, 2012)
Chapman et al. (2012)
+ Tollerud et al. (2012)
Globular clusters
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Huxor et al. (2011, 2012)
Mackey et al. (2009, 2012)
GCs
ECs
Some other results
The M33 stellar halo
McConnachie et al. (2010)
Cockcroft et al. (2012)
Tidal material from the M31/M33 interaction
0Fig.
100 Density
-34 contours
-32 of -30
-28 RGB stars similar to
3.—
candidate
Figure 13 in McConnachie et al. (2010) but updated using data
Genuine M33 stellar halo
Milky Way foreground “contamination”
DGC~30 kpc
Martin et al. (2012)
Fardal et al. (2012)
The remnants of galaxy formation from a panoramic survey of the
region around M31
McConnachie & PAndAS 2009, Nature, 461, 66
PAndAS cubs: Discovery of two new dwarf galaxies in the
surrounding of the Andromeda and Triangulum galaxies
Martin et al. 2009, ApJ, 705, 758
Evidence for an accretion origin for the outer halo globular cluster
system of M31
Mackey et al. 2009, ApJL, 717, 11
The photometric properties of a vast stellar substructure in the
outskirts of M31
McConnachie et al. 2010, ApJ, 723, 1038
The M33 globular clusters with PAndAS data: the last outer halo
clusters?
Cockcroft et al., 2011, ApJ, 730, 112
PAndAS progeny: Extending the M31 dwarf galaxy cabal
Richardson et al., 2011, ApJ, 732, 76
Density variations in the M31 north-west star stream
Carlberg et al, 2011, ApJ, 731, 74
A Bayesian approach to locating the red giant branch tip magnitude
I
Conn et al., 2011, ApJ, 740, 69
A Bayesian approach to locating the red giant branch tip magnitude
II
Conn et al., 2012, ApJ, submitted
The PAndAS view of Andromeda’s dwarf galaxy system I. Automated search and strcutural
properties of the dwarf galaxies
Martin et al. 2012, ApJ, to be submitted
Unearthing foundations of a cosmic cathedral: searching the stars
for M33’s halo
Cockcroft et al. 2012, ApJ, submitted
The non-universal dSph mass profile? A kinematic study of the Andromeda dwarf spheroidal
system
Collins et al. 2012, to be submitted
PAndAS in the Mist: Correlating the stellar and gaseous mass within the halos of M31 and
M33
Lewis, Braun et al. 2012, ApJ, to be submitted
Dynamics in the satellite system of Triangulum: Is And XXII a dwarf satellite of M33?
Chapman et al. 2012, to be submitted
The NGC147-185-CasII sub-group in the Local Group
Irwin et al. 2012, MNRAS, to be submitted
The PAndAS survey catalogue
McConnachie et al. 2013