ROSAT Observations of Compact Groups of Galaxies
Abstract
A search for X-ray emission from compact groups revealed detection from 8 out of the 12 HCG images extracted from the ROSAT public archive. For two of them the X-ray emission originates from galaxies in the group. On the contrary, three groups show an extended emission clearly caused by hot intracluster gas. A Raymond-Smith hot plasma model provides an excellent fit to the X-ray spectra. The estimated temperatures are distributed in a quite narrow range (from 0.73 to 0.92 keV) and are consistent, within the errors, with 0.9 keV. The luminosity ranging from 0.75 to 5.1·1042erg s-1. The most relevant result is the low metal abundance surely detected in two of them and likely in a third that characterizes the hot gas cloud responsible for the X-ray emission. The data concerning the remaining 3 detected compact groups are not sufficient to discriminate with certainty between diffuse and/or point-like X-ray emission. However the results of the spectral analysis point to the presence of a hot gas again with low metal abundance.
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