Galaxy Clusters at the Edge: Temperature, Entropy, and Gas Dynamics at
  the Virial Radius
  Recently, Suzaku has produced temperature and entropy profiles, along with
profiles of gas density, gas fraction, and mass, for multiple galaxy clusters
out to ~r_200 (~= virial radius). In this paper, we compare these novel X-ray
observations with results from N-body + hydrodynamic adaptive mesh refinement
cosmological simulations using the Enzo code. There is excellent agreement in
the temperature, density, and entropy profiles between a sample of 27 mostly
substructure-free massive clusters in the simulated volume and the observed
clusters. This supports our previous contention that clusters have "universal"
outer temperature profiles. Furthermore, it appears that the simplest adiabatic
gas physics used in these Enzo simulations is adequate to model the outer
regions of these clusters without other mechanisms (e.g., non-gravitational
heating, cooling, magnetic fields, or cosmic rays). However, the outskirts of
these clusters are not in hydrostatic equilibrium. There is significant bulk
flow and turbulence in the outer intracluster medium created by accretion from
filaments. Thus, the gas is not fully supported by thermal pressure. The
implications for mass estimation from X-ray data are discussed.
