Probing the dynamical state of galaxy clusters

TL;DR

This paper presents a method to quantitatively assess the hydrostatic equilibrium in galaxy clusters by combining X-ray, SZ, and gravitational lensing data, revealing deviations during mergers.

Contribution

It introduces a novel approach that compares independent mass reconstructions to measure hydrostatic equilibrium without assuming it a priori.

Findings

Method performs well on synthetic data

Hydrostatic equilibrium is violated during mergers

Equilibrium is restored as mergers progress

Abstract

We show how hydrostatic equilibrium in galaxy clusters can be quantitatively probed combining X-ray, SZ, and gravitational-lensing data. Our previously published method for recovering three-dimensional cluster gas distributions avoids the assumption of hydrostatic equilibrium. Independent reconstructions of cumulative total-mass profiles can then be obtained from the gas distribution, assuming hydrostatic equilibrium, and from gravitational lensing, neglecting it. Hydrostatic equilibrium can then be quantified comparing the two. We describe this procedure in detail and show that it performs well on progressively realistic synthetic data. An application to a cluster merger demonstrates how hydrostatic equilibrium is violated and restored as the merger proceeds.