The Intracluster Plasma: a Universal Pressure Profile?

TL;DR

This paper investigates the pressure profiles of intracluster plasma in galaxy clusters, revealing a physical dichotomy into low and high entropy classes and predicting a convergence towards a universal high-entropy profile at higher redshifts.

Contribution

It identifies two main pressure profile patterns linked to entropy states and predicts a systematic evolution towards a universal high-entropy profile at z>0.5.

Findings

Profiles follow two main patterns: steep and shallow.

High redshift clusters show increasing high-entropy prevalence.

Pressure profiles are predicted to converge into a universal high-entropy template.

Abstract

The pressure profiles of the Intracluster Plasma in galaxy clusters show a wide variance when observed in X rays at low redshifts z<0.2. We find the profiles to follow two main patterns, featuring either a steep or a shallow shape throughout both core and outskirts. We trace these shapes back to a physical dichotomy of clusters into two classes, marked by either low entropy (LE) or high entropy (HE) throughout. From X-ray observations and Sunyaev-Zel'dovich stacked data at higher 0.2<z<0.4, we elicit evidence of an increasing abundance of HEs relative to LEs. We propose this to constitute a systematic trend toward high z; specifically, we predict the pressure profiles to converge into a truly universal HE-like template for z>0.5. We submit our physical templates and converging trend for further observational tests, in view of the current and upcoming measurements of individual, stacked, and integrated Sunyaev-Zel'dovich signals.