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 non-baryonic matter and smoothed particle hydrodynamics to model the baryons. 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 ~20% of the simulation; they contain x-ray--luminous diffuse gas well before becoming compact. The component masses, baryon fractions, and gas-to-galaxy mass fractions of the simulated groups are roughly similar somewhat more gas-rich and have x-ray temperatures a factor of 3 lower 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. 
Rachel A. Pildis (1,2), August E. Evrard (1), Joel N. Bregman (1) ((1)   U. Michigan, (2) Center for Astrophysics)