Star formation history and transition epoch of cluster galaxies based on the Horizon-AGN simulation

TL;DR

This study uses the Horizon-AGN simulation to analyze the star formation history of cluster galaxies, revealing environmental effects on low-mass galaxies and defining a transition epoch where cluster galaxies become less active than field galaxies.

Contribution

It provides new insights into the environmental dependence of galaxy quenching and introduces the concept of a transition epoch based on simulation data.

Findings

Low-mass galaxies in clusters have shorter star formation decay times.

Environmental quenching is consistent with ram pressure stripping.

Transition epoch varies with galaxy and cluster mass, earliest at 7.6 Gyr ago.

Abstract

Cluster galaxies exhibit substantially lower star formation rates than field galaxies today, but it is conceivable that clusters were sites of more active star formation in the early universe. Herein, we present an interpretation of the star formation history (SFH) of group/cluster galaxies based on the large-scale cosmological hydrodynamic simulation, Horizon-AGN. We find that massive galaxies in general have small values of e-folding timescales of star formation decay (i.e., ``mass quenching'') regardless of their environment, whilst low-mass galaxies exhibit prominent environmental dependence. In massive host halos (i.e., clusters), the e-folding timescales of low-mass galaxies are further decreased if they reside in such halos for a longer period of time. This ``environmental quenching'' trend is consistent with the theoretical expectation from ram pressure stripping. Furthermore, we define a ``transition epoch'' as where cluster galaxies become less star-forming than field galaxies. The transition epoch of group/cluster galaxies varies according to their stellar and host cluster halo masses. Low-mass galaxies in massive clusters show the earliest transition epoch of $\sim 7.6$ Gyr ago in lookback time. However, it decreases to $\sim 5.2$ Gyr for massive galaxies in low-mass clusters. Based on our findings, we can describe cluster galaxy's SFH with regard to the cluster halo-to-stellar mass ratio.