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

¹ INAF – IASF Milano, Via A. Corti 12, 20133 Milano, Italy
e-mail: marco.balboni@inaf.it
² DiSAT, Università degli Studi dell’Insubria, Via Valleggio 11, 22100 Como, Italy
³ DIFA – Università di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
⁴ INAF – IRA, Via Gobetti 101, 40129 Bologna, Italy
⁵ IRAP, Université de Toulouse, CNRS, CNES, UT3-UPS, 31400 Toulouse, France
⁶ INAF, Osservatorio di Astrofisica e Scienza dello Spazio, Via Piero Gobetti 93/3, 40129 Bologna, Italy
⁷ INFN, Sezione di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy
⁸ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
⁹ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
¹⁰ INFN, Sezione di Roma 2, Università degli Studi di Roma Tor Vergata, Via della Ricerca Scientifica, 1, Roma, Italy
¹¹ Università degli Studi di Roma “Tor Vergata”, Via della Ricerca Scientifica, 1, 00133 Roma, Italy
¹² Dipartimento di Fisica, Universitá degli Studi di Milano, Via G. Celoria 16, 20133 Milano, Italy
¹³ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, LC, Italy
¹⁴ Curtin Institute for Data Science, Curtin University, GPO Box U1987 Perth, WA 6845, Australia

Received: 14 September 2023
Accepted: 21 February 2024

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 only been done 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. In this work, we performed 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 ∼ 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 that 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 fitted a model to the radio emission in the context of turbulent re-acceleration with a constant ratio between thermal and non-thermal particles’ energy densities and a magnetic field profile linked to the thermal gas density as B(r) ∝ n_th^0.5. We found that this simple model cannot reproduce the behaviour of the observed radio emission.