# Detection of anti-correlation of hot and cold baryons in galaxy clusters

## TL;DR

This paper reports the observational detection of an anti-correlation between hot gas and cold stellar matter in galaxy clusters, supporting simulation predictions about baryon distribution.

## Contribution

It provides the first observational evidence of hot and cold baryon anti-correlation in galaxy clusters, using a novel hierarchical Bayesian analysis of multi-wavelength data.

## Key findings

- Detection of anti-correlation consistent with simulations
- Use of hierarchical Bayesian model for analysis
- Analysis of 41 galaxy clusters across multiple wavelengths

## Abstract

The largest clusters of galaxies in the Universe contain vast amounts of dark matter, plus baryonic matter in two principal phases, a majority hot gas component and a minority cold stellar phase comprising stars, compact objects, and low-temperature gas. Hydrodynamic simulations indicate that the highest-mass systems retain the cosmic fraction of baryons, a natural consequence of which is anti-correlation between the masses of hot gas and stars within dark matter halos of fixed total mass. We report observational detection of this anti-correlation based on 4 elements of a $9\times9$ element covariance matrix for nine cluster properties, measured from X-ray, optical, infrared and millimetre wavelength observations of 41 clusters from the Local Cluster Substructure Survey. These clusters were selected using explicit and quantitative selection rules that were then encoded in our hierarchical Bayesian model. Our detection of anti-correlation is consistent with predictions from contemporary hydrodynamic cosmological simulations that were not tuned to reproduce this signal.