Mystery solved: discovery of extended radio emission in the merging galaxy cluster Abell 2146

TL;DR

This study reports the first detection of faint, extended radio emission in galaxy cluster Abell 2146, revealing a radio relic and halo associated with the cluster's merger, showcasing VLA's sensitivity to such structures.

Contribution

First detection of extended radio relic and halo in Abell 2146 using VLA, demonstrating the capability to observe extremely faint radio structures in merging clusters.

Findings

Detected an 850 kpc faint radio structure in Abell 2146.

Identified a radio relic associated with the upstream shock.

Observed a radio halo likely formed shortly after core passage.

Abstract

Abell 2146 ($z=0.232$) is a massive galaxy cluster currently undergoing a spectacular merger in the plane of the sky with a bullet-like morphology. It was the first system in which both the bow and upstream shock fronts were detected at X-ray wavelengths (Mach$\sim2$), yet deep GMRT 325 MHz observations failed to detect extended radio emission associated with the cluster as is typically seen in such systems. We present new, multi-configuration $1-2$ GHz Karl G. Jansky Very Large Array (VLA) observations of Abell 2146 totalling 16 hours of observations. These data reveal for the first time the presence of an extended ($\approx850$ kpc), faint radio structure associated with Abell 2146. The structure appears to harbour multiple components, one associated with the upstream shock which we classify as a radio relic and one associated with the subcluster core which is consisted as being a radio halo bounded by the bow shock. The newly detected structures have some of the lowest radio powers detected thus far in any cluster ($P_{\rm 1.4 GHz, halo}=2.4\pm0.2\times10^{23}$ W Hz$^{-1}$ and $P_{\rm 1.4 GHz, relic}=2.2\pm0.2\times10^{23}$ W Hz$^{-1}$). The flux measurement of the halo, as well as its morphology, also suggest that the halo was recently created ($\approx0.3$ Gyr after core passage), consistent with the dynamical state of the cluster. These observations demonstrate the capacity of the upgraded VLA to detect extremely faint and extended radio structures. Based on these observations, we predict that many more radio relics and radio halos in merging clusters should be detected by future radio facilities such as the Square Kilometre Array (SKA).