nIFTy Galaxy Cluster simulations VI: The dynamical imprint of
  substructure on gaseous cluster outskirts
  Galaxy cluster outskirts mark the transition region from the mildly
non-linear cosmic web to the highly non-linear, virialised, cluster interior.
It is in this transition region that the intra-cluster medium (ICM) begins to
influence the properties of accreting galaxies and groups, as ram pressure
impacts a galaxy's cold gas content and subsequent star formation rate.
Conversely, the thermodynamical properties of the ICM in this transition region
should also feel the influence of accreting substructure (i.e. galaxies and
groups), whose passage can drive shocks. In this paper, we use a suite of
cosmological hydrodynamical zoom simulations of a single galaxy cluster, drawn
from the nIFTy comparison project, to study how the dynamics of substructure
accreted from the cosmic web influences the thermodynamical properties of the
ICM in the cluster's outskirts. We demonstrate how features evident in radial
profiles of the ICM (e.g. gas density and temperature) can be linked to strong
shocks, transient and short-lived in nature, driven by the passage of
substructure. The range of astrophysical codes and galaxy formation models in
our comparison are broadly consistent in their predictions (e.g. agreeing when
and where shocks occur, but differing in how strong shocks will be); this is as
we would expect of a process driven by large-scale gravitational dynamics and
strong, inefficiently radiating, shocks. This suggests that mapping such shock
structures in the ICM in a cluster's outskirts (via e.g. radio synchrotron
emission) could provide a complementary measure of its recent merger and
accretion history.
