AAS 207th Meeting, 8-12 January 2006
Session 89 Dwarf Galaxies: Stellar Distributions and Star Formation
Oral, Tuesday, 10:00-11:30am, January 10, 2006, Salon 3

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[89.03] Faint Stellar Systems: Ultra-Luminous Globular Clusters and Ultra-Compact Dwarf Galaxies

M. Hasegan (Rutgers University)

Detailed studies of globular clusters in our Galaxy and other Local Group galaxies have revealed that these old star clusters trace a fundamental plane that is analogous to, but distinct from, the one for elliptical galaxies. Support for a universal formation mechanism would come if GCs in environments outside of the Local Group obeyed the same scaling relations.

A potentially new type of faint and compact stellar system has recently been identified in the Fornax Cluster, called ultra-compact dwarf galaxies (UCDs). The properties of a handful of UCDs have inspired a number of different scenarios for their origin. Reliable information on an expanded sample of UCD candidates, and on the exceptionally bright GCs which are underrepresented in the Local Group, is needed to understand the evolutionary links, if any, between these faint stellar system. We have examined the dynamics and kinematics of compact, high-luminosity globular cluster candidates associated with M87 and other early-type galaxies in the Virgo Cluster. Our observational dataset included high-resolution spectroscopy from Keck-ESI and HST imaging - taken as part of the ACS Virgo Cluster Survey in ~ Sloan g and z filters and WFPC2 V-band archival data.

Among the investigated objects, we found ``normal'' globular clusters which follow the scaling relations of their Galactic counterparts, as well as larger and more massive ``ultra-compact dwarfs" which resemble the nuclei of nucleated dwarf elliptical galaxies and may contain dark matter. One additional object may be an old ``stellar supercluster'', formed through the amalgamation of multiple young massive clusters.

This work was done in collaboration with the ACS Virgo Cluster Survey team. Support for this program was provided mainly by the Space Telescope Science Institute, Association of Universities for Research in Astronomy, Inc., National Aeronautics and Space Administration and National Science Foundation.

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