Henry Ferguson STScI August 28, 2008 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

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 Covers 0.2 Mpc2 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?

Nuclei are slightly redder than the surrounding galaxy Grant et al. 2005

Virgo Fornax

Cote et al. 2006

Lisker et al. 2006

Virgo Cluster dE shapes (SDSS)

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 Coma-cluster 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