The Properties of Galaxies in X-ray Bright and Faint Groups

Abstract

Galaxy groups are an intermediate density environment in which more than half of the galaxies in the local universe reside. Galaxy groups have a small contrast against the vast background of galaxies and therefore until recently it has remained very difficult to identify large samples. Using observational data from the Group Environment and Evolution Collaboration (GEEC) and the Cosmological Evolution Survey (COSMOS) new calculations of passive fractions and disk fractions for galaxies in X-ray bright and faint groups are investigated. How these fractions depend on the overall environment, galaxy stellar mass, total group mass, group-centric distance, group X-ray luminosity and redshift is examined. It was found that the passive and disk fractions were different in X-ray bright and faint groups and depend most strongly on galaxy stellar mass, redshift and overall environment with less dependence on the other parameters. Attempts to connect the star formation and morphology results are made. The results show that the passive fractions were higher in X-ray groups yet the disk fractions were also found to be higher in these groups. This was a surprising result as disk-like galaxies are typically associated with star-forming galaxies. The results show the complexity within galaxy groups.