Hydrodynamic simulations of correlation and scatter in galaxy cluster maps

TL;DR

This paper uses hydrodynamical simulations to compare X-ray and Sunyaev-Zel'dovich maps of galaxy clusters, revealing how clumpiness affects their correlation and scatter, and proposing methods to characterize deviations.

Contribution

It introduces a comparison framework for cluster maps from simulations and observations, highlighting the role of clumpiness and pseudo-entropy in understanding map deviations.

Findings

X-ray pseudo-pressure is a good proxy for SZ maps.

Clumpiness causes deviations between X-ray and SZ maps.

Pseudo-entropy maps effectively characterize clumpiness.

Abstract

The two dimensional structure of hot gas in galaxy clusters contains information about the hydrodynamical state of the cluster, which can be used to understand the origin of scatter in the thermodynamical properties of the gas, and to improve the use of clusters to probe cosmology. Using a set of hydrodynamical simulations, we provide a comparison between various maps currently employed in the X-ray analysis of merging clusters and those cluster maps anticipated from forthcoming observations of the thermal Sunyaev-Zel'dovich effect. We show the following: 1) an X-ray pseudo-pressure, defined as square root of the soft band X-ray image times the temperature map is a good proxy for the SZ map; 2) we find that clumpiness is the main reason for deviation between X-ray pseudo-pressure and SZ maps; 3) the level of clumpiness can be well characterized by X-ray pseudo-entropy maps. 4) We describe the frequency of deviation in various maps of clusters as a function of the amplitude of the deviation. This enables both a comparison to observations and a comparison to effects of introduction of complex physical processes into simulation.