PROPERTIES OF SIMULATED COMPACT-GROUPS OF GALAXIES

We analyze compact groups of galaxies appearing in a galaxy formation simulation dominated by cold dark matter (Omega(0)=1, Omega(baryon)=0. 1). The simulation uses an N-body code to model the behavior of the no n-baryonic matter and smoothed particle hydrodynamics to model the bar yons. One run includes gas dynamics alone, and the other incorporates star formation as well. Groups identified as physically compact at z=0 form originally along filaments and become compact in the final simil ar to 20% of the simulation; they contain x-ray-luminous diffuse gas w ell before becoming compact. The component masses, baryon fractions, a nd gas-to-galaxy mass fractions of the simulated groups are roughly si milar to those of Hickson compact groups (HCGs), although they tend to be somewhat more gas rich and have x-ray temperatures a factor of 3 l ower than those seen in HCGs. These discrepancies may be alleviated by adding the effects of energy input into the diffuse group gas by star formation and supernovae. (C) 1996 American Astronomical Society.