ROSAT Observations of Compact Groups of Galaxies
Session 5 -- ROSAT Observations of Clusters and Groups
Display presentation, Wednesday, January 12, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[5.02] ROSAT Observations of Compact Groups of Galaxies

R.A. Pildis, J.N. Bregman, A.E. Evrard (U. Michigan)

We have analyzed ROSAT PSPC observations of several compact groups of galaxies for diffuse $10^6$ K gas in the group potential. The detection of such gas would indicate that these groups are not simply a result of chance superposition, and would allow a determination of the total mass and baryonic fraction of a small number of interacting galaxies.

We find that diffuse X-ray gas is relatively rare in the groups we analyzed, even though deep optical imaging reveals that the galaxies in most of these groups appear to be interacting with one another. Some of the individual galaxies do show enhanced X-ray emission relative to isolated galaxies of the same type, however. The diffuse hot gas---when it exists---tends to be centered on the brightest elliptical galaxy (or, in the case of HCG 62, the two overlapping bright ellipticals) in the group. Our reanalysis of the ROSAT observation of the NGC 2300 group shows only very weak diffuse emission with a smaller $\beta$ and a smaller radial extent than previously reported. This increases the baryon fraction of this group to a value consistent with that found previously in other groups.