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Session 38 - Dwarf Galaxies.
Display session, Tuesday, January 14
Metropolitan Ballroom,

[38.05] HST Dwarf Elliptical Galaxy Snapshot Survey

B. W. Miller (DTM/STScI), H. C. Ferguson, M. Stiavelli, B. C. Whitmore (STScI)

Dwarf elliptical galaxies are the most common type of galaxy in the universe, yet their formation and early evolution remain a mystery. We present preliminary results of a Hubble Space Telescope snapshot survey of dE galaxies in the Virgo and Fornax Clusters and the Leo Group which will provide important information on the properties of the nuclei and globular cluster systems of dE galaxies. Among more luminous galaxies, the specific frequency of globular clusters varies from S_N \approx 4 for ellipticals to S_N < 1 for late type spirals and irregulars. A measure of S_N for dE galaxies therefore provides a fairly straightforward test of whether dE's are true low-luminosity ellipticals, or simply dwarf irregulars (dI's) that have lost their gas. Further goals of the project are to test the universality of the globular cluster luminosity function; (2) to look for evidence of recent formation of the nuclei; and (3) to look for clues to why the globular cluster specific frequency varies greatly from galaxy to galaxy. With roughly half of our sample observed we already have some intriguing results for dE galaxies with M_B<-13. Our preliminary finding confirms the high values of S_N reported from ground-based surveys, suggesting that dE galaxies are more closely related to giant E's than late-type spirals or irregulars. The results further suggest nucleated dE's have higher globular cluster specific frequencies, S_N, than non-nucleated dE's. The high resolution of HST also allows us to more accurately classify the galaxies; several galaxies that had been classified as non-nucleated from ground-based observations are now known to be nucleated. Finally, many of the nuclei, or brightest globular clusters, are offset from the geometrical centers of the galaxies.

Program listing for Tuesday