AAS 207th Meeting, 8-12 January 2006
Session 80 Evolution of Galaxies, Galaxies Surveys II
Poster, Tuesday, 9:20am-6:30pm, January 10, 2006, Exhibit Hall

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[80.04] VICS: Stellar Populations of a Dwarf Spheroidal Galaxy in the Virgo Cluster

P.R. Durrell (YSU), B.F. Williams, R.B. Ciardullo (Penn State), J.J. Feldmeier (NOAO/YSU), G.H. Jacoby (WIYN), S. Sigurdsson (Penn State), T. von Hippel (U.Texas), H. Ferguson (STScI), N. Tanvir (U.Hertfordshire), M. Arnaboldi (Torino Obs./ESO), O. Gerhard (MPE Garching), A. Aguerri (IAC), K. Freeman (Mt. Stromlo), M. Vinciguerra (Penn State)

We report the discovery of a very low-luminosity (MV ~ -10) dwarf galaxy in the Virgo Cluster within the ACS field of the VICS Project (Ciardullo et al.). The galaxy, which is ~1 kpc in extent, is clearly resolved into stars, and provides us with the first direct look at the stellar population of a low-luminosity system in a galaxy cluster. A F606W-F814W color-magnitude diagram of the cluster's brightest ~250 stars is dominated by a clearly defined red-giant branch (RGB), which reaches ~ 1.5 magnitudes down from the RGB tip. The colors of the RGB stars are suggestive of a very metal-poor object, and the absolute magnitude of the RGB tip, F814W(VegaMag) ~ 27.2, confirms that the object is a member of the Cluster. The size, luminosity, and central surface brightness of this galaxy are similar to those of typical dSph galaxies in the Local Group.

Support for this work was provided by NASA through grant number GO-10131 from the Space Telescope Science Institute.

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