Cosmology and Astrophysics from Relaxed Galaxy Clusters III: Thermodynamic Profiles and Scaling Relations

TL;DR

This study analyzes thermodynamic profiles and scaling relations of 40 relaxed galaxy clusters, revealing that simple models work well outside centers but complex processes influence inner regions, with implications for cluster physics and cosmology.

Contribution

It provides detailed thermodynamic profiles and scaling relations for relaxed galaxy clusters, incorporating intrinsic scatter and covariance, and highlights the importance of heating and cooling processes in cluster cores.

Findings

Thermodynamic profiles are regular with small scatter outside centers.

Inner regions show departures from spherical symmetry due to heating and cooling.

Profiles suggest a tight feedback loop regulating cluster atmospheres.

Abstract

This is the third in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters. Our sample comprises 40 clusters identified as being dynamically relaxed and hot (i.e., massive) in Papers I and II of this series. Here we consider the thermodynamics of the intracluster medium, in particular the profiles of density, temperature and related quantities, as well as integrated measurements of gas mass, average temperature, total luminosity and center-excluded luminosity. We fit power-law scaling relations of each of these quantities as a function of redshift and cluster mass, which can be measured precisely and with minimal bias for these relaxed clusters using hydrostatic arguments. For the thermodynamic profiles, we jointly model the density and temperature and their intrinsic scatter as a function of radius, thus also capturing the behavior of the gas pressure and entropy. For the integrated quantities, we also jointly fit a multidimensional intrinsic covariance. Our results reinforce the view that simple hydrodynamical models provide a good description of relaxed clusters outside their centers, but that additional heating and cooling processes are important in the inner regions (radii $r < 0.5r_{2500} \approx 0.15r_{500}$). The thermodynamic profiles remain regular, with small intrinsic scatter, down to the smallest radii where deprojection is straightforward ($\sim 20$ kpc); within this radius, even the most relaxed systems show clear departures from spherical symmetry. Our results suggest that heating and cooling are continuously regulated in a tight feedback loop, allowing the cluster atmosphere to remain stratified on these scales.