Constraining the magnetic field in the galaxy cluster Abell 2142 using MeerKAT L-band polarisation data

¹ Dipartimento di Fisica e Astronomia, Università di Bologna, Via Piero Gobetti 93/2, I-40129 Bologna, Italy
² INAF – Istituto di Radioastronomia di Bologna, Via Piero Gobetti 101, I-40129 Bologna, Italy
³ Astronomisches Institut der Ruhr-Universität Bochum (AIRUB), Universitätsstraße 150, 44801 Bochum, Germany
⁴ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, Selargius, Italy

^⋆ Corresponding author: annalisa.pagliotta@unibo.it

Received: 31 March 2025
Accepted: 28 June 2025

Abstract

Context. Magnetic fields permeate the Universe, including galaxy clusters, and affect the thermodynamical properties of the intra-cluster medium (ICM). Cosmological simulations predict that structure formation and mergers are capable of amplifying seed magnetic fields up to the μG level in the ICM, but the magnetic field strength and structure have only been studied in a few clusters.

Aims. Abell 2142 is a local massive warm-cool-core cluster that shows evidence of a post-merger dynamical state. It hosts a multi-component radio halo and features both embedded and background polarised radio galaxies. In this work, we aim to constrain the magnetic field intensity, radial profile, and power spectrum within its ICM, providing key insights into the nature of this non-thermal component in galaxy clusters.

Methods. We present MeerKAT observations of Abell 2142 in the L-band (872−1712 MHz), imaged in polarisation for the first time with this purpose. We derived the rotation measure (RM) from the polarised emission of radio galaxies by applying the RM synthesis technique and analyse both the RM and fractional polarisation (F_p). To investigate the magnetic field distribution within the ICM, we compared our results with mock RM maps generated from 3D simulations of the cluster.

Results. We find that the RM dispersion, σ_RM, decreases with the projected radius, whereas the F_p increases. Both trends suggest that the magnetic field intensity decreases at larger distances from the cluster centre, in agreement with studies of other clusters. Assuming the magnetic field energy density scales with the gas thermal energy (B ∝ n_e^0.5), we find the best fit to our data is a magnetic field with a power spectrum ranging between 7 and 470 kpc, with peak at ∼140 kpc and mean central strength of 9.5 ± 1.0 μG.

Conclusions. The high central magnetic field lies at the upper end of the range observed in other systems and supports the possibility of an hadronic contribution to the diffuse radio emission previously detected at the cluster centre.