Chandra X-ray observations of Abell 1835 to the virial radius

TL;DR

This study presents the first Chandra X-ray observations reaching the virial radius of galaxy cluster Abell 1835, revealing a steep temperature decline and potential non-equilibrium gas states at large radii.

Contribution

First detection of X-ray emission out to the virial radius in Abell 1835, analyzing temperature profiles and gas stability at large cluster radii.

Findings

Temperature drops by a factor of ten from core to virial radius

Gas is convectively unstable at outskirts

Data suggest presence of warm-hot gas or clumping at large radii

Abstract

We report the first Chandra detection of emission out to the virial radius in the cluster Abell 1835 at z=0.253. Our analysis of the soft X-ray surface brightness shows that emission is present out to a radial distance of 10 arcmin or 2.4 Mpc, and the temperature profile has a factor of ten drop from the peak temperature of 10 keV to the value at the virial radius. We model the Chandra data from the core to the virial radius and show that the steep temperature profile is not compatible with hydrostatic equilibrium of the hot gas, and that the gas is convectively unstable at the outskirts. A possible interpretation of the Chandra data is the presence of a second phase of warm-hot gas near the cluster's virial radius that is not in hydrostatic equilibrium with the cluster's potential. The observations are also consistent with an alternative scenario in which the gas is significantly clumped at large radii.