Leavers and remainers: Galaxies split by group-exit

TL;DR

This study investigates how galaxy groups are disrupted in clusters, revealing that most satellites are quickly stripped from their hosts during their first close approach, affecting cluster substructure.

Contribution

It provides new insights into the dynamics of satellite disruption and the timing of substructure formation in galaxy clusters.

Findings

92.2% of satellites leave their host after pericentre within half a Gyr.

Most satellites are unbound and at large distances post-pericentre, complicating their identification.

Substructure is mostly on first infall, especially extended satellites beyond R200.

Abstract

The disruption of substructure in galaxy clusters likely plays an important role in shaping the cluster population as a significant fraction of cluster galaxies today have spent time in a previous host system, and thus may have been pre-processed. Once inside the cluster, group galaxies face the combined environmental effects from group and cluster - so called 'post-processing'. We investigate these concepts, by tracking the evolution of satellites and their hosts after entering the cluster and find that tidal forces during their first pericentric passage are very efficient at breaking up groups, preferentially removing satellites at larger distances from their hosts. 92.2% of satellites whose host has passed pericentre will leave their host by $z=0$, typically no later than half a Gyr after pericentric passage. We find satellites leave with high velocities, and quickly separate to large distances from their hosts, making their identification within the cluster population challenging. Those few satellites ($\sim$7.8%) that remain bound to their hosts after a pericentric passage are typically found close to their host centres. This implies that substructure seen in clusters today is very likely on first infall into the cluster, and yet to pass pericentre. This is even more likely if the substructure is extended, with satellites beyond R$_{200}$ of their host. We find the cluster dominates the tidal mass loss and destruction of satellites, and is responsible for rapidly halting the accretion of new satellites onto hosts once they reach 0.6-0.8 R$_{200}$ radii from the cluster.