Are X-ray properties of loose groups different from those of compact groups?

Abstract

We compare the X-ray properties of loose and compact galaxy groups, using a combined sample of 42 groups. We find that we are unable to separate loose and compact groups on the luminosity-temperature relation, the luminosity-velocity dispersion relation or the velocity dispersion-temperature relation using equally weighted errors. This suggests that the distinction between compact and loose groups is not a fundamental one, and we argue that a more useful distinction is that between X-ray bright and X-ray faint systems. Given their similarity in X-ray properties, we combine the loose and compact subsamples to derive relations based on the full sample. This provides the highest statistical quality results to date on the way in which the correlations in X-ray properties of low mass systems depart from those seen in rich clusters.