Comparing galaxy morphology and star formation properties in X-ray bright and faint groups and clusters

Galaxy morphologies and star formation rates depend on environment. Galaxies in underdense regions are generally star-forming and discy whereas galaxies in overdense regions tend to be early-type and not actively forming stars. The mechanism(s) responsible for star formation quenching and morphological transformation remain unclear, although many processes have been proposed. We study the dependence of star formation and morphology on X-ray luminosity for galaxies in Sloan Digital Sky Survey Data Release 7 (SDSS-DR7) groups and clusters. While controlling for stellar and halo mass dependences, we find that galaxies in X-ray strong groups and clusters have preferentially low star-forming and disc fractions – with the differences being strongest at low stellar masses. The trends that we observe do not change when considering only galaxies found within or outside of the X-ray radius of the host group. When considering central and satellite galaxies separately we find that this dependence on X-ray luminosity is only present for satellites, and we show that our results are consistent with ‘galaxy strangulation’ as a mechanism for quenching these satellites. We investigate the dynamics of the groups and clusters in the sample, and find that the velocity distributions of galaxies beyond the virial radius in low X-ray luminosity haloes tend to be less Gaussian in nature than the rest of the data set. This may be indicative of low X-ray luminosity groups and clusters having enhanced populations of star-forming and disc galaxies as a result of recent accretion.