Galaxy cluster outskirts: a universal entropy profile for relaxed clusters?

TL;DR

This paper investigates whether a universal entropy profile describes relaxed galaxy cluster outskirts, comparing observational data with theoretical models and simulations, and finds discrepancies suggesting additional physics beyond gas clumping.

Contribution

It proposes a universal entropy profile for relaxed galaxy clusters and evaluates existing models against observational data, highlighting the limitations of gas clumping explanations.

Findings

Universal entropy profile fits data well outside 0.3r200

Discrepancies between observations and simulations in outskirts

Gas clumping alone cannot explain entropy flattening

Abstract

We fit a functional form for a universal ICM entropy profile to the scaled entropy profiles of a catalogue of X-ray galaxy cluster outskirts results, which are all relaxed cool core clusters at redshift below 0.25. We also investigate the functional form suggested by Lapi et al. and Cavaliere et al. for the behaviour of the entropy profile in the outskirts and find it to fit the data well outside 0.3r200 . We highlight the discrepancy in the entropy profile behaviour in the outskirts between observations and the numerical simulations of Burns et al., and show that the entropy profile flattening due to gas clumping calculated by Nagai & Lau is insufficient to match observations, suggesting that gas clumping alone cannot be responsible for all of the entropy profile flattening in the cluster outskirts. The entropy profiles found with Suzaku are found to be consistent with ROSAT, XMM-Newton and Planck results.