A giant radio bridge connecting two clusters in Abell 1758

TL;DR

This study reports the discovery of a giant radio bridge connecting two galaxy clusters in Abell 1758, revealing early-stage non-thermal phenomena during cluster collision.

Contribution

First detailed radio observation of a large-scale bridge between pre-merging galaxy clusters, expanding understanding of early collision phases.

Findings

Radio bridge confirmed at 144 MHz, tentatively at 53 MHz.

Bridge's radio emissivity is over ten times lower than cluster halos.

Radio and X-ray emissions in the bridge are correlated.

Abstract

Collisions between galaxy clusters dissipate enormous amounts of energy in the intra-cluster medium (ICM) through turbulence and shocks. In the process, Mpc-scale diffuse synchrotron emission in form of radio halos and relics can form. However, little is known about the very early phase of the collision. We used deep radio observations from 53 MHz to 1.5 GHz to study the pre-merging galaxy clusters A1758N and A1758S that are $\sim2$ Mpc apart. We confirm the presence of a giant bridge of radio emission connecting the two systems that was reported only tentatively in our earlier work. This is the second large-scale radio bridge observed to date in a cluster pair. The bridge is clearly visible in the LOFAR image at 144 MHz and tentatively detected at 53 MHz. Its mean radio emissivity is more than one order of magnitude lower than that of the radio halos in A1758N and A1758S. Interestingly, the radio and X-ray emissions of the bridge are correlated. Our results indicate that non-thermal phenomena in the ICM can be generated also in the region of compressed gas in-between infalling systems.