uGMRT and MeerKAT observation of RXCJ0232-4420: a quiet cluster with a giant radio halo

TL;DR

This study presents the first multi-frequency spectral analysis of the galaxy cluster RXCJ0232--4420, revealing a giant radio halo and a candidate relic, and discusses implications for cluster dynamics and particle re-acceleration.

Contribution

It provides the first detailed spectral and morphological analysis of a giant radio halo in a cool-core cluster using uGMRT and MeerKAT data, highlighting turbulence-driven re-acceleration.

Findings

The radio halo extends over 1 Mpc, confirming it as a giant radio halo.

A candidate relic of about 300 kpc was detected east of the cluster.

The spectral index of the halo is approximately -1.17, with a mostly uniform spectral map.

Abstract

Giant radio halos are the Mpc-scale extended sources associated with the merging clusters, while the mini-halos are preferentially associated with cool-core clusters. Both trace the ICM plasma physical process, and recent low-frequency observations increasingly blur the distinction between the two classes. We present the first multi-frequency spectral analysis of the galaxy cluster RXCJ0232--4420, hosting a cool core, using uGMRT (400 and 650 MHz) and MeerKAT (1283 MHz) observations. The central radio emission extends beyond $\sim 1$ Mpc at all frequencies, confirming it as a giant radio halo. One candidate relic (in the east) has also been detected, with an extent of $\sim 300$ kpc. The integrated spectral indices of halo and candidate east relic are $\alpha = -1.17 \pm 0.17$, and $\alpha = -0.85 \pm 0.17$, respectively. The resolved spectral map of the halo is mostly uniform ($-1.0$ to $-1.3$) and does not show any radial steepening. The radio surface brightness profile is well modelled by a single exponential law, with the e-folding radius constant across frequencies. The radio halo emission is morphologically well correlated with the thermal emission. Point-to-point radio-X-ray correlation analysis gives a sublinear relationship (slope $\sim 0.80$), with no frequency evolution. The presence of Mpc-scale emission in the cool-core cluster shows that such emission can arise in dynamically intermediate systems. Our results demonstrate that merger-driven turbulence, even from minor disturbances, can sustain cluster-wide particle re-acceleration without destroying the cool core.