Transcript Galaxy Evolution Science in the Era of PanSTARRS and LSST

Dwarf Elliptical Galaxies in the Coma
Cluster from the HST Treasury Survey
or
Clusters in Dwarfs in Clusters
Henry Ferguson
STScI
August 28, 2008
Open Questions
• Are dE just E galaxies in smaller halos?
• Or are they stripped irregulars/spirals?
• Do dE properties depend on environment?
• Are dE and dSph the same beast?
• Did dE’s in clusters form earlier? Survive longer?
• Why do there appear to be more dE’s per E+S0 in richer
groups than in poorer ones?
• What are dE nuclei?
• How do they relate to black holes in more massive
galaxies?
• Are they the progenitors of some GC’s? UCDs?
Cluster dwarfs and the missing satellites
• No missing satellite problem for Virgo
– Whatever solutions work for the local-group must
not break Virgo
– True dwarfs probably vastly outnumber remnants
of stripped giant galaxies
• Cluster dwarfs may survive longer
– Some dwarfs that would otherwise merge with the
central galaxy in their halo are tidally liberated
when that halo merges into a larger halo
– Not obvious that cluster dE’s should have same
sizes, ages, etc as satellite dE’s.
The HST Coma Cluster Treasury Program
David Carter (PI)
Alfonso Aguerri
Marc Balcells
Dan Batcheldor
Terry Bridges
Jonathan Davies
Peter Erwin
Harry C. Ferguson
Paul Goudfrooij
Alister W. Graham
Rafael Guzman
Ann Hornschemeier
Michael J Hudson
Shardha Jogee
Yutaka Komiyama
Jennifer Lotz
John Lucey
David Merritt
Bryan Miller
Neal A. Miller
Bahram Mobasher
Mustapha Mouhcine
Sadanori Okamura
Reynier F. Peletier
Steve Phillipps
Bianca Poggianti
Thomas H. Puzia
Ray M. Sharples
Russell Smith
Neil Trentham
R. Brent Tully
Edwin Valentijn
Survey objectives
• Luminosity Function to MV ~ -9.
• Morphologies for a wide range of luminosity and
environment.
• Colors and color gradients in a wide range of luminosity and
environment.
• Bright and faint ends of the global scaling laws.
• C-M diagrams for globular clusters.
• Detection of Ultra-Compact Dwarfs (UCDs)
• Morphology of “E+A” galaxies
• Selection of samples on surface brightness and
morphological criteria for spectroscopy.
Cycle 15 survey
F475W and F814W
82 fields planned
(900 sq. arcmin)
42 fields in central
mosaic
40 centered on known
members in the
outskirts
Supporting
observations:
Hectospec
DEIMOS
Subaru
VLA …
Observed
before ACS
failed:
25 fields
(275 sq. arcmin)
Focus on nuclei…
• Resolution ~50 parsecs at Coma
• Comparable to the best ground-based resolution for Virgo
• Cluster dE are relatively easy to distinguish from
background galaxies by morphology alone
• It’s possible to see and measure the nuclei
• Covers 0.2 Mpc2
• (Compared to 0.02 Mpc2 for the HST Virgo Cluster survey)
• ~500 eyeball-classified members
Properties of dE nuclei
• Nuclei represent <10% of the total light
(typically ~ 2%)
• Nuclear magnitude increases with galaxy magnitude
• Generally brighter than globular clusters
• Radii
• r1/2 in Virgo range from 60 to 2 pc (median 4 pc)
• Colors
• Color-luminosity relation
• On average redder than surrounding galaxy, with large
scatter
• Some blue ones
• Velocity Dispersions
• ~10-50 km/s in the brighter ones
Universal “CMO” relation?
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Nuclei are slightly redder than the
surrounding galaxy
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Grant et al. 2005
Virgo
Fornax
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Cote et al.
2006
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Lisker et al. 2006
Virgo Cluster dE shapes (SDSS)
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Coma Treasury Bright dE,N
Bright dE
Fainter dE,N
Fainter dE
Fainter dE,N
Fainter dE
Nuclei tend to be in brighter dE
(selection?)
dE,N
dE
Spatial segregation
Spatial segregation
Strongly nucleated
Weakly nucleated
Throwing out weakly nucleated dE’s…
Throwing out weakly nucleated dE’s…
K-S test probability < 3% (bright dE vs dE,N)
Colors (preliminary!)
Colors of bright dE
K-S test probability 5%
Conclusions
• Central nuclear star clusters are common in Comacluster dE
• Trends for Virgo and Fornax appear to hold in Coma:
– Brighter dE’s tend to have nuclei
– dE,N population is strongly concentrated toward the cluster
center
– Bright dE population is less strongly concentrated
• Hint of a color difference at fixed mag for bright dE?
• dE with no nuclei are a younger infalling population
• dE,N and most of the faint dE are an old, relaxed
population
– survivors of early formation of the cluster