MeerKAT L-band observations of the Ophiuchus galaxy cluster

Detection of synchrotron threads and jellyfish galaxies

¹ INAF – IRA, Via P. Gobetti 101, 40129 Bologna, Italy
² Dipartimento di Fisica e Astronomia, Università di Bologna, Via P. Gobetti 93/2, 40129 Bologna, Italy
³ INAF – IASF Milano, Via A. Corti 12, 20133 Milano, Italy
⁴ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands

^⋆ Corresponding author: andrea.botteon@inaf.it

Received: 21 March 2025
Accepted: 18 April 2025

Abstract

Context. Observations with modern radio interferometers are uncovering the intricate morphology of synchrotron sources in galaxy clusters, both those arising from the intracluster medium and those associated with member galaxies. Moreover, in addition to the well-known radio tails from active galactic nuclei, radio continuum tails from jellyfish galaxies are being efficiently detected in nearby clusters and groups.

Aims. Our goal is to investigate the radio emission from the Ophiuchus cluster, a massive sloshing cluster in the local Universe (z = 0.0296) that hosts a diffuse mini halo at its center.

Methods. To achieve this, we analyzed a 7.25 h MeerKAT L-band observation, producing sensitive images at 1.28 GHz with multiple resolutions. A catalog of spectroscopically confirmed cluster galaxies was used to identify and study the member galaxies detected in radio.

Results. We discover thin threads of synchrotron emission embedded in the mini halo, two of which may be connected to the brightest cluster galaxy. We also report the first identification of jellyfish galaxies in Ophiuchus, detecting six galaxies with radio continuum tails, one of which extends for ∼64 kpc at 1.28 GHz, making it one of the longest detected at such a high frequency. Finally, we propose an alternative scenario to explain the origin of a bright amorphous radio source, previously classified as a radio phoenix, aided by the comparison with recent simulations of radio jets undergoing kink instability.

Conclusions. In Ophiuchus, thin threads have been observed within the diffuse emission; a similar result was obtained in Perseus, another nearby cluster hosting a mini halo, suggesting that these structures may be a common feature in this kind of source. Moreover, radio continuum observations have proven effective in detecting the first jellyfish galaxies in both systems.