Model-Independent Limits on the Line-of-Sight Depth of Clusters of Galaxies Using X-ray and Sunyaev-Zel'dovich Data

TL;DR

This paper presents a model-independent method to determine the minimum line-of-sight depth of galaxy cluster plasma using X-ray and SZ data, applicable across various temperatures and metallicities, with application to the Bullet Cluster.

Contribution

It introduces a new model-independent approach to constrain the line-of-sight extent of galaxy clusters using combined X-ray and SZ observations.

Findings

Lower limit of 400 +/- 56 kpc on the half-pressure depth of the Bullet Cluster

Method applicable for plasma temperatures between 0.3 keV and 20 keV

Constraints suggest the cluster is at least spherical along the line of sight

Abstract

We derive a model-independent expression for the minimum line-of-sight extent of the hot plasma in a cluster of galaxies. The only inputs are the 1-5 keV X-ray surface brightness and the Comptonization from Sunyaev-Zel'dovich (SZ) data. No a priori assumptions regarding equilibrium or geometry are required. The method applies when the X-ray emitting material has temperatures anywhere between 0.3 keV and 20 keV and metallicities between 0 and twice solar---conditions fulfilled by nearly all intracluster plasma. Using this method, joint APEX-SZ and Chandra X-ray Observatory data on the Bullet Cluster yield a lower limit of 400 +/- 56 kpc on the half-pressure depth of the main component, limiting it to being at least spherical, if not cigar-shaped primarily along the line of sight.