The amazing diversity in the hot gas content of an X-ray unbiased massive galaxy clusters sample

TL;DR

This study reveals a vast intrinsic diversity in the X-ray luminosity of galaxy clusters at a fixed mass, highlighting a broader population than previously observed in X-ray or SZ surveys.

Contribution

The paper presents a new, X-ray unbiased sample of galaxy clusters with dynamically estimated masses, enabling an unbiased assessment of intracluster medium variability.

Findings

Clusters show up to 50-fold variation in X-ray luminosity at fixed mass.

Dispersion in X-ray luminosity at fixed mass is approximately 0.5 dex.

Sample includes clusters with low surface brightness, expanding known cluster diversity.

Abstract

We aim to determine the intrinsic variety, at a given mass, of the properties of the intracluster medium in clusters of galaxies. This requires a cluster sample selected independently of the intracluster medium content for which reliable masses and subsequent X-ray data can be obtained. We present one such sample, consisting of 34 galaxy clusters selected independently of their X-ray properties in the nearby ($0.050<z<0.135$) Universe and mostly with $14<\log M_{500}/M_\odot \lesssim 14.5$, where masses are dynamically estimated. We collected the available X-ray observations from the archives and then observed the remaining clusters with the low-background Swift X-ray telescope, which is extremely useful for sampling a cluster population expected to have low surface brightness. We found that clusters display a large range (up to a factor 50) in X-ray luminosities within $r_{500}$ at a given mass, whether or not the central emission ($r<0.15 r_{500}$) is excised, unveiling a wider cluster population than seen in Sunayev-Zeldovich surveys or inferred from the population seen in X-ray surveys. The measured dispersion is $0.5$ dex in $L_X$ at a given mass.