Disturbed galaxy clusters are more abundant in an X-ray volume-limited sample

TL;DR

This study provides observational evidence that biases in the apparent abundance of relaxed galaxy clusters are due to survey selection methods, not intrinsic properties, highlighting the importance of considering cluster morphology for accurate scaling relations.

Contribution

It demonstrates that the X-ray cool-core bias is absent in a volume-limited sample, attributing previous biases to survey selection effects rather than cluster nature.

Findings

Biases are due to survey selection, not intrinsic cluster properties.

Relaxed and disturbed clusters have distinct X-ray luminosity distributions.

A 60% displacement aligns the luminosity distributions of different cluster types.

Abstract

We present first strong observational evidence that the X-ray cool-core bias or the apparent bias in the abundance of relaxed clusters is absent in our REFLEX volume-limited sample (ReVols). We show that these previously observed biases are due to the survey selection method such as for an flux-limited survey, and are not due to the inherent nature of X-ray selection. We also find that the X-ray luminosity distributions of clusters for the relaxed and for the disturbed clusters are distinct and a displacement of approximately 60 per cent is required to match two distributions. Our results suggest that to achieve more precise scaling relation one may need to take the morphology of clusters and their fractional abundance into account.