A ROSAT SURVEY OF WICKSONS COMPACT GALAXY GROUPS

We report the results of an almost complete survey of the X-ray proper ties of Hickson's compact galaxy groups with the ROSAT PSPC. Diffuse X -ray emission is detected from 22 groups. We infer that hot intragroup gas is present in greater than or similar to 75 per cent of these sys tems, and derive their X-ray luminosity function. Earlier reports that only spiral-poor systems exhibit diffuse X-ray emission are found Co be incorrect. Strong correlations are found between the X-ray luminosi ty and both the gas temperature and the velocity dispersion of the gro up galaxies. We argue that these properties provide strong evidence th at most of these groups are genuinely compact configurations, rather t han line-of-sight superpositions. Comparison with the X-ray properties of galaxy clusters indicates a significant steepening of the L-T rela tion below T similar to 1 KeV, which may result from tile action of ga laxy winds.