Hydrodynamic Simulation of Non-thermal Pressure Profiles of Galaxy
  Clusters
  Cosmological constraints from X-ray and microwave observations of galaxy
clusters are subjected to systematic uncertainties. Non-thermal pressure
support due to internal gas motions in galaxy clusters is one of the major
sources of astrophysical uncertainties. Using a mass-limited sample of galaxy
clusters from a high-resolution hydrodynamical cosmological simulation, we
characterize the non-thermal pressure fraction profile and study its dependence
on redshift, mass, and mass accretion rate. We find that the non-thermal
pressure fraction profile is universal across redshift when galaxy cluster
radii are defined with respect to the mean matter density of the universe
instead of the commonly used critical density. We also find that the
non-thermal pressure is predominantly radial, and the gas velocity anisotropy
profile exhibits strong universality when galaxy cluster radii are defined with
respect to the mean matter density of the universe. However, we find that the
non-thermal pressure fraction is strongly dependent on the mass accretion rate
of the galaxy cluster. We provide fitting formulae for the universal
non-thermal pressure fraction and velocity anisotropy profiles of gas in galaxy
clusters, which should be useful in modeling astrophysical uncertainties
pertinent to using galaxy clusters as cosmological probes.
