X-ray observations of the galaxy cluster PKS 0745-191: To the virial radius, and beyond

TL;DR

This study uses Suzaku X-ray observations to measure the properties of the galaxy cluster PKS 0745-191 out to 1.5 times its virial radius, revealing temperature decline and entropy profile flattening, informing models of cluster physics.

Contribution

First measurements of cluster outskirts beyond the virial radius, providing new insights into intracluster medium properties and cluster assembly processes.

Findings

Temperature decreases by ~70% from 0.3 to 1 r_200

Entropy profile flattens near the virial radius

Gas fraction and mass estimates are affected by non-hydrostatic effects

Abstract

We measure X-ray emission from the outskirts of the cluster of galaxies PKS 0745-191 with Suzaku, determining radial profiles of density, temperature, entropy, gas fraction, and mass. These measurements extend beyond the virial radius for the first time, providing new information about cluster assembly and the diffuse intracluster medium out to ~1.5 r_200, (r_200 ~ 1.7 Mpc ~ 15'). The temperature is found to decrease by roughly 70 per cent from 0.3-1 r_200. We also see a flattening of the entropy profile near the virial radius and consider the implications this has for the assumption of hydrostatic equilibrium when deriving mass estimates. We place these observations in the context of simulations and analytical models to develop a better understanding of non-gravitational physics in the outskirts of the cluster.