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

TL;DR

This study examines how galaxy star-formation and morphology vary with X-ray luminosity in groups and clusters, revealing that X-ray strong environments suppress star formation especially in satellite galaxies, supporting the galaxy strangulation mechanism.

Contribution

It provides new evidence linking X-ray luminosity of galaxy groups to star-formation suppression, emphasizing the role of environment in galaxy evolution.

Findings

Galaxies in X-ray strong groups have lower star-forming and disk fractions.

The dependence on X-ray luminosity is significant only for satellite galaxies.

Low X-ray luminosity groups show less Gaussian velocity distributions, indicating recent accretion.

Abstract

Galaxy morphologies and star-formation rates depend on environment. Galaxies in under-dense regions are generally star-forming and disky 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 dependencies, we find that galaxies in X-ray strong groups and clusters have preferentially low star-forming and disk 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 stangulation" 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 halos 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 disk galaxies as a result of recent accretion.