Radio observations of the merging galaxy cluster system Abell 3391-Abell 3395

TL;DR

This study uses radio and X-ray observations to investigate the merging galaxy clusters Abell 3391 and Abell 3395, finding no diffuse radio emission in the X-ray bridge but identifying numerous large radio galaxies and potential relics.

Contribution

First comprehensive radio and X-ray analysis of Abell 3391-Abell 3395, providing upper limits on diffuse emission and cataloging large radio galaxies and relic candidates.

Findings

No diffuse radio emission detected in the X-ray bridge region.

Identified 20 giant radio galaxies with sizes >1 Mpc, increasing known density.

Found 7 candidates for cluster radio relics and halos.

Abstract

The pre-merging system of galaxy clusters Abell 3391-Abell 3395 located at a mean redshift of 0.053 has been observed at 1 GHz in an ASKAP/EMU Early Science observation as well as in X-rays with eROSITA. The projected separation of the X-ray peaks of the two clusters is $\sim$50$'$ or $\sim$ 3.1 Mpc. Here we present an inventory of interesting radio sources in this field around this cluster merger. While the eROSITA observations provide clear indications of a bridge of thermal gas between the clusters, neither ASKAP nor MWA observations show any diffuse radio emission coinciding with the X-ray bridge. We derive an upper limit on the radio emissivity in the bridge region of $\langle J \rangle_{1\,{\rm GHz}}< 1.2 \times 10^{-44} {\rm W}\, {\rm Hz}^{-1} {\rm m}^{-3}$. A non-detection of diffuse radio emission in the X-ray bridge between these two clusters has implications for particle-acceleration mechanisms in cosmological large-scale structure. We also report extended or otherwise noteworthy radio sources in the 30 deg$^2$ field around Abell 3391-Abell 3395. We identified 20 Giant Radio Galaxies, plus 7 candidates, with linear projected sizes greater than 1 Mpc. The sky density of field radio galaxies with largest linear sizes of $>0.7$ Mpc is $\approx 1.7$ deg$^{-2}$, three times higher than previously reported. We find no evidence for a cosmological evolution of the population of Giant Radio Galaxies. Moreover, we find seven candidates for cluster radio relics and radio halos.