Leavers and remainers: galaxies split by group-exit

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 (∼ 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.

The Three Hundred Project: Substructure in hydrodynamical and dark matter simulations of galaxy groups around clusters

“…The phase space of group members in our dark matteronly simulations is in agreement with the distribution found by Choque-Challapa et al (2019), despite their use of lower mass clusters (∼ 10 14 h −1 M ), and a lower limit on satellite masses (∼ 10 7.8 h −1 M ). The greatest concentration of subhaloes in this phase space is close to the line representing the boundness criterion, spread between approximately 0.7R grp,h 200 and 1.5R grp,h 200 , with the maximum located at r = 1.1R grp,h 200 , v = vcir.…”

“…Only 9% of dark matter-only groups contain at least one subhalo with r < 0.3R grp,h 200 and v < vcir (excluding the host halo at the centre of each group). This is a region that previous work, such as that of Choque-Challapa et al (2019), has also shown to contain few satellites in dark matter-only simulations.…”

“…In Section 3.1, we identify galaxy groups located in the region we refer to as the 'cluster outskirts', between[R clus,h 200 , 5R clus,h 200 ] from the cluster centre at z = 0. Then, in Section 3.2, we instead identify infalling galaxy groups, at all redshifts, again using the same methods asHan et al (2018) andChoque-Challapa et al (2019). Using the halo merger trees, we first identify all objects that have just fallen into the cluster, taken from the whole history of the cluster; that is, we find galaxies that were at a distance greater than R clus,h 200 from the cluster centre in one snapshot, but are within R clus,h 200 in the following snapshot.…”

Compact Groups of Galaxies in Sloan Digital Sky Survey and LAMOST Spectral Survey. I. The Catalogs

“…On the other hand, it is also possible that these embedded CGs are gravitationally bound sub-systems recently falling into large clusters. In this case, the dynamics of their members could be partially heated but still be kinematically colder than the host clusters (e.g., Choque-Challapa et al 2019;Benavides et al 2020)).…”

“…This result indicates that these outer CGs, at least, might consist of (or include) newly-accreted groups. Indeed, numerical simulations (e.g., Cohn 2012;Choque-Challapa et al 2019) have predicted that these newly accreted systems have not passed through the cluster center and are mainly located at the outskirts of host clusters. Despite of experiencing dynamical heating, these sub-systems remain dynamically colder and more compact than the host cluster (Benavides et al 2020).…”