Mass Accretion and its Effects on the Self-Similarity of Gas Profiles in
  the Outskirts of Galaxy Clusters
  Galaxy clusters exhibit remarkable self-similar behavior which allows us to
establish simple scaling relationships between observable quantities and
cluster masses, making galaxy clusters useful cosmological probes. Recent X-ray
observations suggest that self-similarity may be broken in the outskirts of
galaxy clusters. In this work, we analyze a mass-limited sample of massive
galaxy clusters from the Omega500 cosmological hydrodynamic simulation to
investigate the self-similarity of the diffuse X-ray emitting intracluster
medium (ICM) in the outskirts of galaxy clusters. We find that the
self-similarity of the outer ICM profiles is better preserved if they are
normalized with respect to the mean density of the universe, while the inner
profiles are more self-similar when normalized using the critical density.
However, the outer ICM profiles as well as the location of accretion shock
around clusters are sensitive to their mass accretion rate, which causes the
apparent breaking of self-similarity in cluster outskirts. We also find that
the collisional gas does not follow the distribution of collisionless dark
matter perfectly in the infall regions of galaxy clusters, leading to 10%
departures in the gas-to-dark matter density ratio from the cosmic mean value.
Our results have a number implications for interpreting observations of galaxy
clusters in X-ray and through the Sunyaev-Zel'dovich effect and their
application to cluster cosmology.
