Intracluster gas pressure, entropy injection and redshift evolution

TL;DR

This paper models how entropy injection affects the intracluster medium's pressure profile, showing that combined preheating and in situ heating are necessary to match observations and predicting how these processes evolve with redshift.

Contribution

It introduces a simple universal prescription for entropy injection that reproduces observed pressure profiles and extends the model to high redshift clusters, predicting entropy injection evolution.

Findings

Both preheating and in situ heating are required for the universal pressure profile.

Entropy injection decreases with redshift, scaling as (1+z)^{-0.8}.

Current data suggest entropy injection was lower at earlier times.

Abstract

We study the effect of entropy injection in the intracluster medium (ICM) in light of the recent observationally determined universal pressure profile of the ICM. Beginning with a power-law entropy profile that is expected in the absence of any feedback, we show that a simple universal prescription of entropy injection results in the final, observed universal pressure profile. This simple prescription has two components, one associated with an overall increase in entropy and another associated with injection in the central parts of the cluster. Importantly, both the components of entropy injection are needed to produce the final universal pressure profile. This is indicative of a need of both preheating the ICM as well {\it in situ} AGN/SNe heating. We demonstrate the usefulness of the method by extending the calculations to clusters at high redshift, and predict redshift evolution of cluster scaling relations that can be tested against data. We show that the self-similar evolution of the universal pressure profile is equivalent to a negative evolution of entropy injection with redshift, with a scaling $S_{inj} \propto (1+z)^{-0.8} S_{inj}(z=0)$. We also show the current observational data are indicative of the entropy injection decreasing with redshift.