nIFTy galaxy cluster simulations V: Investigation of the Cluster Infall
  Region
  We examine the properties of the galaxies and dark matter haloes residing in
the cluster infall region surrounding the simulated $\Lambda$CDM galaxy cluster
studied by Elahi et al. (2016) at z=0. The
$1.1\times10^{15}h^{-1}\text{M}_{\odot}$ galaxy cluster has been simulated with
eight different hydrodynamical codes containing a variety of hydrodynamic
solvers and subgrid schemes. All models completed a dark-matter only,
non-radiative and full-physics run from the same initial conditions. The
simulations contain dark matter and gas with mass resolution
$m_{\text{DM}}=9.01\times 10^8h^{-1}\text{M}_{\odot}$ and
$m_{\text{gas}}=1.9\times 10^8h^{-1}\text{M}_{\odot}$ respectively. We find
that the synthetic cluster is surrounded by clear filamentary structures that
contain ~60% of haloes in the infall region with mass ~$10^{12.5} - 10^{14}
h^{-1}\text{M}_{\odot}$, including 2-3 group-sized haloes ($>
10^{13}h^{-1}\text{M}_{\odot}$). However, we find that only ~10% of objects in
the infall region are subhaloes residing in haloes, which may suggest that
there is not much ongoing preprocessing occurring in the infall region at z=0.
By examining the baryonic content contained within the haloes, we also show
that the code-to-code scatter in stellar fraction across all halo masses is
typically ~2 orders of magnitude between the two most extreme cases, and this
is predominantly due to the differences in subgrid schemes and calibration
procedures that each model uses. Models that do not include AGN feedback
typically produce too high stellar fractions compared to observations by at
least ~1 order of magnitude.
