# Hydrostatic Chandra X-ray analysis of SPT-selected galaxy clusters - I. Evolution of profiles and core properties

## TL;DR

This study uses Chandra X-ray data and a new modeling code to analyze galaxy cluster profiles, finding no significant evolution in core properties or entropy distribution over a broad redshift range.

## Contribution

It introduces MBProj2, a new forward-modeling projection code, and applies it to study the evolution of galaxy cluster core properties with no evidence of significant change.

## Key findings

- No evidence for a central entropy floor in low-entropy systems.
- The entropy distribution peaks near zero and around 130 keV cm^2.
- No significant evolution of core properties with redshift.

## Abstract

We analyse Chandra X-ray Observatory observations of a set of galaxy clusters selected by the South Pole Telescope using a new publicly-available forward-modelling projection code, MBProj2, assuming hydrostatic equilibrium. By fitting a powerlaw plus constant entropy model we find no evidence for a central entropy floor in the lowest-entropy systems. A model of the underlying central entropy distribution shows a narrow peak close to zero entropy which accounts for 60 per cent of the systems, and a second broader peak around 130 keV cm^2. We look for evolution over the 0.28 to 1.2 redshift range of the sample in density, pressure, entropy and cooling time at 0.015 R_500 and at 10 kpc radius. By modelling the evolution of the central quantities with a simple model, we find no evidence for a non-zero slope with redshift. In addition, a non-parametric sliding median shows no significant change. The fraction of cool-core clusters with central cooling times below 2 Gyr is consistent above and below z=0.6 (~30-40 per cent). Both by comparing the median thermodynamic profiles, centrally biased towards cool cores, in two redshift bins, and by modelling the evolution of the unbiased average profile as a function of redshift, we find no significant evolution beyond self-similar scaling in any of our examined quantities. Our average modelled radial density, entropy and cooling-time profiles appear as powerlaws with breaks around 0.2 R_500. The dispersion in these quantities rises inwards of this radius to around 0.4 dex, although some of this scatter can be fit by a bimodal model.