  In the current epoch, one of the main mechanisms driving the growth of galaxy
clusters is the continuous accretion of group-scale halos. In this process, the
ram pressure applied by the hot intracluster medium on the gas content of the
infalling group is responsible for stripping the gas from its dark-matter halo,
which gradually leads to the virialization of the infalling gas in the
potential well of the main cluster. Using deep wide-field observations of the
poor cluster Hydra A/A780 with XMM-Newton and Suzaku, we report the discovery
of an infalling galaxy group 1.1 Mpc south of the cluster core. The presence of
a substructure is confirmed by a dynamical study of the galaxies in this
region. A wake of stripped gas is trailing behind the group over a projected
scale of 760 kpc. The temperature of the gas along the wake is constant at kT ~
1.3 keV, which is about a factor of two less than the temperature of the
surrounding plasma. We observe a cold front pointing westwards compared to the
peak of the group, which indicates that the group is currently not moving in
the direction of the main cluster, but is moving along an almost circular
orbit. The overall morphology of the group bears remarkable similarities with
high-resolution numerical simulations of such structures, which greatly
strengthens our understanding of the ram-pressure stripping process.
