AAS 203rd Meeting, January 2004
Session 51 Galaxy Groups and Nearby Clusters
Poster, Tuesday, January 6, 2004, 9:20am-6:30pm, Grand Hall

## [51.04] Dwarf galaxies in Hickson Compact Groups

E. Krusch, D.J. Bomans, R.-J. Dettmar (Astronomisches Institut Ruhr-Universität Bochum, Germany), C. Taylor (U. Massachusetts)

Hickson Compact Groups (HCGs) are excellent laboratories for the study of the influence of the environment on member galaxies. We identified dwarf galaxies in the outer regions of HCGs with the intention to investigate the unknown evolutionary status of these groups using dwarf glaxies as a tracer. This is possible, because they are the most common type of galaxies and the environment influences their evolution. In order to establish the dwarf galaxy content of such groups, we observed a sample of five HCGs (16, 19, 30, 31, 42) with the WFI (0.\circ54 \times 0.\circ57) at the ESO/MPIA 2.2\,m telescope at La Silla and found more than 2000 new dwarf galaxy candidates in each group. In order to determine dwarf elliptical (dE) galaxies belonging to the CGs we used the red sequence of the Color Magnitude Diagram and additionally morphology, radial profile, and the surface brightness of the candidate galaxies. \\ From these results it is possible to draw the conclusion that the CGs of our sample are not chance configurations but physically bound systems where dE galaxies have evolved due to the influence of their surroundings. The density distribution of these galaxies decreases from the center to the limits of our mosaic data. In all of our HCGs the dwarf galaxy members extend far beyond the density centers of cataloged CGs. Using velocity information of a subsample we calculated the radius of the zero--velocity--surface, beyond which galaxies participate in the Hubble expansion. We determined the approximate extension of the groups and the relation of the compact core to a possible extended halo and derived typical radii, which are of the order of 2\,Mpc indicating sizes similar to large galaxy groups. This result suggests that the large galaxies of HCGs are centers of larger loose groups.