The Destruction of a Compact Group of Galaxies

Abstract

The very high apparent galaxy densities in Hickson compact groups (HCGs) should produce copious amounts of galaxy-galaxy interaction, if these groups are bound dynamical units. I examine the evidence for such interactions in HCG 94, a group of seven galaxies with an envelope of diffuse optical light and an extremely high X-ray luminosity. Using $ROSAT$ HRI data and deep three-color optical imaging of the group, I find that both the hot ($k$T $\sim$ 4 keV) gas and the diffuse optical light trace the same elongated potential well, which is offset from the galaxy distribution. The luminosity and colors of the diffuse optical light imply that the group galaxies are being ripped apart to form a cD-type remnant galaxy. The similarity in shape of the X-ray and optical contours may mean that this destruction process may require several billion years.