The uncommon intracluster medium features of the first massive clusters selected independently of their baryon content

TL;DR

This study investigates four galaxy clusters selected by weak gravitational lensing, revealing that they exhibit more rare and unique features than expected from traditional ICM-selected samples, highlighting potential biases in current cluster studies.

Contribution

It demonstrates that unbiased, lensing-selected clusters show more uncommon features, challenging the representativeness of ICM-selected samples for understanding cluster thermodynamics.

Findings

Clusters show on average two rare features per property.

Unbiased selection reveals more uncommon cluster features.

Biases in ICM-selected samples may overlook diverse cluster properties.

Abstract

Our current knowledge of the thermodynamic properties of galaxy clusters comes primarily from detailed studies of clusters selected by their minority components: hot baryons. Most of these studies select the clusters using the component that is being investigated, the intracluster medium (ICM), making the sample choice prone to selection effects. Weak-gravitational lensing allows us to select clusters by the total mass component and, being independent of the type of matter, makes the sample choice unbiased with respect to the baryon content. In this paper, we study four galaxy clusters at intermediate redshift ($0.25<z<0.61$), selected from the weak-lensing survey of Miyazaki et al. (2018). We derive core-excised X-ray luminosities, richness-based masses, Compton parameters, and profiles of mass, pressure and electron densities. These quantities are derived from shear data, Compton maps, and our own X-ray and SZ follow-up. When compared to ICM-selected clusters of the same mass, in the range $2$ to $5 \ 10^{14}$ M$_\odot$, our small sample of four clusters is expected to have on average 0.2 rare ($>2\sigma$) features, while we observed on average two rare features in each one of the seven explored properties: richness, core-excised luminosity, Compton parameter, pressure and electron pressure profiles, and central values of them. The abundance of rare and unique features in such a small sample indicates a fundamental bias in our knowledge of the thermodynamic properties of clusters when derived from ICM-selected samples.