Ultra-Compact Dwarfs in the Coma Cluster
  We have undertaken a spectroscopic search for ultra compact dwarf galaxies
(UCDs) in the dense core of the dynamically evolved, massive Coma cluster as
part of the HST/ACS Coma Cluster Treasury Survey. UCD candidates were initially
chosen based on color, magnitude, degree of resolution within the ACS images,
and the known properties of Fornax and Virgo UCDs. Follow-up spectroscopy with
Keck/LRIS confirmed 27 candidates as members of the Coma Cluster, a success
rate > 60% for targeted objects brighter than M_R = -12. Another 14 candidates
may also prove to be Coma members, but low signal-to-noise spectra prevent
definitive conclusions. An investigation of the properties and distribution of
the Coma UCDs finds these objects to be very similar to UCDs discovered in
other environments. The Coma UCDs tend to be clustered around giant galaxies in
the cluster core and have colors/metallicity that correlate with the host
galaxy. With properties and a distribution similar to that of the Coma cluster
globular cluster population, we find strong support for a star cluster origin
for the majority of the Coma UCDs. However, a few UCDs appear to have stellar
population or structural properties which differentiate them from the old star
cluster populations found in the Coma cluster, perhaps indicating that UCDs may
form through multiple formation channels.
