Shock and Splash: Gas and Dark Matter Halo Boundaries around LambdaCDM
  Galaxy Clusters
  Recent advances in simulations and observations of galaxy clusters suggest
that there exists a physical outer boundary of massive cluster-size dark matter
haloes. In this work, we investigate the locations of the outer boundaries of
dark matter and gas around cluster-size dark matter haloes, by analyzing a
sample of 65 massive dark matter halos extracted from the Omega500 zoom-in
hydrodynamical cosmological simulations. We show that the location of accretion
shock is offset from that of the dark matter splashback radius, contrary to the
prediction of the self-similar models. The accretion shock radius is larger
than all definitions of the splashback radius in the literature by 20-100%. The
accretion shock radius defined using the steepest drop in the entropy pressure
profiles is approximately 2 times larger than the splashback radius defined by
the steepest slope in the dark matter density profile, and it is ~1.2 times
larger than the edge of the dark matter phase-space structure. We discuss
implications of our results for multi-wavelength studies of galaxy clusters.
