Feedback, scatter and structure in the core of the PKS 0745-191 galaxy cluster

TL;DR

This study uses Chandra X-ray data to analyze the core of galaxy cluster PKS 0745-191, revealing feedback mechanisms, cold fronts, and thermodynamic fluctuations, and introduces a new analysis code for cluster profiles.

Contribution

The paper presents a new code, MBPROJ, for accurately deriving thermodynamic profiles of galaxy clusters from X-ray data, accounting for deviations from equilibrium and symmetry.

Findings

X-ray cavities indicate powerful AGN feedback.

Density, temperature, and pressure fluctuations are quantified.

Evidence suggests deviations from hydrostatic equilibrium in the core.

Abstract

We present Chandra X-ray Observatory observations of the core of the galaxy cluster PKS 0745-191. Its centre shows X-ray cavities caused by AGN feedback and cold fronts with an associated spiral structure. The cavity energetics imply they are powerful enough to compensate for cooling. Despite the evidence for AGN feedback, the Chandra and XMM-RGS X-ray spectra are consistent with a few hundred solar masses per year cooling out of the X-ray phase, sufficient to power the emission line nebula. The coolest X-ray emitting gas and brightest nebula emission is offset by around 5 kpc from the radio and X-ray nucleus. Although the cluster has a regular appearance, its core shows density, temperature and pressure deviations over the inner 100 kpc, likely associated with the cold fronts. After correcting for ellipticity and projection effects, we estimate density fluctuations of ~4 per cent, while temperature, pressure and entropy have variations of 10-12 per cent. We describe a new code, MBPROJ, able to accurately obtain thermodynamical cluster profiles, under the assumptions of hydrostatic equilibrium and spherical symmetry. The forward-fitting code compares model to observed profiles using Markov Chain Monte Carlo and is applicable to surveys, operating on 1000 or fewer counts. In PKS0745 a very low gravitational acceleration is preferred within 40 kpc radius from the core, indicating a lack of hydrostatic equilibrium, deviations from spherical symmetry or non-thermal sources of pressure.