Testing Strict Hydrostatic Equilibrium in Simulated Clusters of Galaxies: Implications to Abell 1689

TL;DR

This study investigates the validity of hydrostatic equilibrium in galaxy clusters, revealing significant non-thermal pressure contributions that impact mass estimates, especially in the core regions, with implications for cosmological measurements.

Contribution

The paper demonstrates that non-thermal pressure significantly affects mass estimates in galaxy clusters, challenging the assumption of strict hydrostatic equilibrium used in X-ray analyses.

Findings

Non-thermal pressure contributes 20%-45% near cluster centers.

In relaxed clusters, non-thermal support increases with radius, reaching 30%-45% at Rvir.

In Abell 1689, non-thermal pressure accounts for about 40% of the core pressure.

Abstract

Accurate mass determination of clusters of galaxies is crucial if they are to be used as cosmological probes. However, there are some discrepancies between cluster masses determined based on gravitational lensing, and X-ray observations assuming strict hydrostatic equilibirium (i.e., the equilibrium gas pressure is provided entirely by thermal pressure). Cosmological simulations suggest that turbulent gas motions remaining from hierarchical structure formation may provide a significant contribution to the equilibrium pressure in clusters. We analyze a sample of massive clusters of galaxies drawn from high resolution cosmological simulations, and find a significant contribution (20%-45%) from non-thermal pressure near the center of relaxed clusters, and, in accord with previous studies, a minimum contribution at about 0.1 Rvir, growing to about 30%-45% at the virial radius, Rvir. Our results strongly suggest that relaxed clusters should have significant non-thermal support in their core region. As an example, we test the validity of strict hydrostatic equilibirium in the well-studied massive galaxy cluster Abell 1689 using the latest high resolution gravitational lensing and X-ray observations. We find a contribution of about 40% from non-thermal pressure within the core region of A1689, suggesting an alternate explanation for the mass discrepancy: the strict hydrostatic equilibirium is not valid in this region.