  Galaxy clusters grow by accreting galaxies as individual objects, or as
members of a galaxy group. These groups can strongly impact galaxy evolution,
stripping the gas from galaxies, and enhancing the rate of galaxy mergers.
However, it is not clear how the dynamics and structure of groups are affected
when they interact with a large cluster, or whether all group members
necessarily experience the same evolutionary processes. Using data from
TheThreeHundred project, a suite of 324 hydrodynamical resimulations of large
galaxy clusters, we study the properties of 1340 groups passing through a
cluster. We find that half of group galaxies become gravitationally unbound
from the group by the first pericentre, typically just 0.5-1 Gyr after cluster
entry. Most groups quickly mix with the cluster satellite population; only 8%
of infalling group haloes later leave the cluster, although for nearly half of
these, all of their galaxies have become unbound, tidally disrupted or merged
into the central by this stage. The position of galaxies in group-centric phase
space is also important -- only galaxies near the centre of a group
($r\lesssim0.7R_{200}$) remain bound once a group is inside a cluster, and
slow-moving galaxies in the group centre are likely to be tidally disrupted, or
merge with another galaxy. This work will help future observational studies to
constrain the environmental histories of group galaxies. For instance, groups
observed inside or nearby to clusters have likely approached very recently,
meaning that their galaxies will not have experienced a cluster environment
before.
