Differences in the Physical Properties of Satellite Galaxies within Relaxed and Disturbed Galaxy Groups and Clusters

TL;DR

This study uses simulations to compare satellite galaxy properties in relaxed versus disturbed galaxy clusters, revealing that disturbed clusters have more blue, star-forming galaxies due to higher gas availability, with star formation initially boosted then suppressed during mergers.

Contribution

It provides a detailed analysis of how the dynamical state of galaxy clusters influences satellite galaxy properties using state-of-the-art simulations.

Findings

Disturbed clusters have more blue, star-forming satellites.

Gas availability is higher in disturbed clusters.

Star formation is boosted early in cluster mergers then suppressed.

Abstract

Galaxy groups and clusters are the most massive collapsed structures in the Universe. Those structures are formed by collapsing with other smaller structures. Groups and cluster mergers provide an appropriate environment for the evolution and transformation of their galaxies. The merging process of groups and clusters can affect the properties of their galaxy populations. Our aim is to characterise the distribution of galaxies' colour, specific star formation rate, quenched galaxy fraction, and gas availability in galaxies bounded to groups and clusters and to examine how these properties relate to the dynamical state of their host environments. We used the most massive halos ($M > 10^{13} M_{\odot}$) in Illustris TNG100 simulations and separated the sample into two categories: relaxed and disturbed halos. This classification was done based on the offset between the position of the Brightest Cluster Galaxy (BCG) and the centre of mass of the gas. Subsequently, we classified their galaxy populations into red and blue galaxies using a threshold derived from a double Gaussian fit to their colour distribution. Our findings reveal differences in physical properties such as colour, star formation rates, and gas availability among satellite galaxies bound to interacting clusters compared to relaxed clusters. Disturbed clusters exhibit more blue, star-forming galaxies than their relaxed counterparts. This discrepancy in the fraction of blue and star-forming galaxies can be attributed to higher gas availability, including hot, diffuse, and condensed gas in satellite galaxies in disturbed clusters compared to relaxed ones. Furthermore, our study shows that during cluster mergers, there are two crucial phases; at the beginning of the interaction, there is an important boost in the star formation rate followed by suppression as the cluster reaches the equilibrium state.