  We present analysis of bulk and random gas motions in the intracluster medium
using high-resolution Eulerian cosmological simulations of sixteen simulated
clusters, including both very relaxed and unrelaxed systems and spanning a
virial mass range of 5*10^13 - 2*10^15 Msun/h. We investigate effects of the
residual subsonic gas motions on the hydrostatic estimates of mass profiles and
concentrations of galaxy clusters. In agreement with previous studies we find
that the gas motions contribute up to ~ 5%-15% of the total pressure support in
relaxed clusters with contribution increasing with cluster-centric radius. The
fractional pressure support is higher in unrelaxed systems. This contribution
would not be accounted for in hydrostatic estimates of the total mass profile
and would lead to systematic underestimate of mass. We demonstrate that total
mass can be recovered accurately if pressure due to gas motions measured in
simulations is explicitly taken into account in the equation of hydrostatic
equilibrium. Given that the underestimate of mass is increasing at larger
radii, where gas is less relaxed and contribution of gas motions to pressure is
larger, the total density profile derived from hydrostatic analysis is more
concentrated than the true profile. This may at least partially explain some
high values of concentrations of clusters estimated from hydrostatic analysis
of X-ray data.
