PAndAS mining the stellar halo of Andromeda - Stellar streams, dwarf galaxies, globular clusters et al.
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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
๏ Largescale 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
๏ Largescale 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
๏ Isthere a faint end to galaxy
formation?
• sensitive to star-formation-
500 kpc
suppression mechanisms M31
• “missing satellite crisis”?
๏ Which dark matter halos
contain stars?
• What sets their numbers? their
properties (luminosity, size,
shape)? Springel et al. (2009)
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
PAndAS data
๏ Observing 3 mag. below the
Galactic halo
tip of RGB
Galactic disk
• 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
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 kpcMeasuring Shape/Lumpiness of the halo
• Ibata et al. (2012) 150 kpc
• McConnachie et al. (2012/13)
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
Metal-poor
-383 M31 RGBs
HI gas
-300
-300
-247
-417
-240 -280
-180The M31 satellite systems PAndAS’ Cubs: Dwarf galaxies & globular clusters
Zucker et al. (2004; 1) Cas II
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)
6 dSphs (2004) → 28 dSphs (now;
4 SDSS + 16 PAndAS)
Tri I + deep follow-up760
Two examples MARTIN ET AL.
Martin et al. (2009)
Vol. 705
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
Y
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.
X
(A color version of this figure is available in the online journal.)
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 IBayesian TRGB distance analysisA. Conn et al. (2011, 2012)
550
kpc 950 300 900 300 1000Bayesian distance analysis
A. Conn et al. (2011, 2012)
Homogeneous c)
distancesAutomatic search & completeness limits
Martin et al. (2012)
๏ Fullstatistical analysis of
spatial + CMD information
• Accounting for varying MW
foreground contamination,
very structured M31
“contamination”Automatic search & completeness limits
Martin et al. (2012)
๏ Fullstatistical analysis of
spatial + CMD information
• Accounting for varying MW
foreground contamination,
detection S/N
very structured M31 XII
“contamination”
๏ Automated search: XI
• completeness function as XIII
f(X,Y,rh,[Fe/H],m-M,…) M06 GC
• new candidate dwarf
galaxies
→ comparison with simulationsDwarf galaxy radial velocities Collins et al. (2011, 2012)
Chapman et al. (2012)
i n s ’
l l
o ’s
C
le row
h e l
ic i d
e M ry W
se Lar
d
a ters!
n
p o s
+ Tollerud et al. (2012)Globular clusters Huxor et al. (2011, 2012)
Mackey et al. (2009, 2012)
y
e ste’s r s !
c k
a po
a l M r ’s
u g
o Hu xo
e D n
s e Av o
an d
GCs
ECsSome other results
The M33 stellar halo McConnachie et al. (2010)
Cockcroft et al. (2012)
Tidal material from the M31/M33 interaction Genuine M33 stellar halo
0Fig. 100 Density
3.— -34 contours
-32 of -30 -28 RGB stars similar to
candidate
Figure 13 in McConnachie et al. (2010) but updated using dataMilky Way foreground “contamination”
Martin et al. (2012)
Fardal et al. (2012)
DGC~30 kpcThe 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 The PAndAS view of Andromeda’s dwarf galaxy system I. Automated search and strcutural
II properties of the dwarf galaxies
Conn et al., 2012, ApJ, submitted Martin et al. 2012, ApJ, to be submitted
Unearthing foundations of a cosmic cathedral: searching the stars The non-universal dSph mass profile? A kinematic study of the Andromeda dwarf spheroidal
for M33’s halo system
Cockcroft et al. 2012, ApJ, submitted Collins et al. 2012, to be submitted
PAndAS in the Mist: Correlating the stellar and gaseous mass within the halos of M31 and Dynamics in the satellite system of Triangulum: Is And XXII a dwarf satellite of M33?
M33 Chapman et al. 2012, to be submitted
Lewis, Braun et al. 2012, ApJ, to be submitted
The NGC147-185-CasII sub-group in the Local Group
The PAndAS survey catalogue
Irwin et al. 2012, MNRAS, to be submitted McConnachie et al. 2013You can also read
