Residual Gas Motions in the Intracluster Medium and Bias in Hydrostatic Measurements of Mass Profiles of Clusters

TL;DR

This study uses high-resolution simulations to analyze gas motions in galaxy clusters, revealing their impact on mass estimates and potential biases in hydrostatic measurements, especially at larger radii.

Contribution

It quantifies the contribution of gas motions to pressure support and demonstrates how accounting for these motions improves mass profile accuracy.

Findings

Gas motions contribute 5-15% of total pressure in relaxed clusters.

Unrelaxed systems show higher fractional pressure support from gas motions.

Ignoring gas motions leads to underestimation of cluster masses and overestimation of concentration parameters.

Abstract

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.