CHEX-MATE: A LOFAR pilot X-ray$-$radio study on five radio halo clusters

TL;DR

This study combines X-ray and radio data for five galaxy clusters to analyze the spatial relationship between thermal and non-thermal properties, revealing correlations and differences based on cluster dynamical states.

Contribution

It provides the first spatially resolved analysis of thermal and non-thermal properties in galaxy clusters using combined CHEX-MATE and LOFAR data, testing a turbulent re-acceleration model.

Findings

Strong correlation between radio and X-ray surface brightness (r_s ~ 0.7).

Less disturbed clusters show peaked central radio profiles with outer flattening.

The simple turbulent re-acceleration model cannot fully explain observed radio emission behaviors.

Abstract

The connection between the thermal and non-thermal properties in galaxy clusters hosting radio halos seems fairly well established. However, a comprehensive analysis of such a connection has been made only for integrated quantities (e.g. $L_X - P_{radio}$ relation). In recent years new-generation radio telescopes have enabled the unprecedented possibility to study the non-thermal properties of galaxy clusters on a spatially resolved basis. Here, we perform a pilot study to investigate the mentioned properties on five targets, by combining X-ray data from the CHEX-MATE project with the second data release from the LOFAR Two meter Sky survey. We find a strong correlation ($r_s \sim 0.7$) with a slope less than unity between the radio and X-ray surface brightness. We also report differences in the spatially resolved properties of the radio emission in clusters which show different levels of dynamical disturbance. In particular, less perturbed clusters (according to X-ray parameters) show peaked radio profiles in the centre, with a flattening in the outer regions, while the three dynamically disturbed clusters have steeper profiles in the outer regions. We fit a model to the radio emission in the context of turbulent re-acceleration with a constant ratio between thermal and non-thermal particles energy density and a magnetic field profile linked to the thermal gas density as $B(r) \propto n_{th}^{0.5}$. We found that this simple model cannot reproduce the behaviour of the observed radio emission.