Discovery of a Radio Relic in the Massive Merging Cluster SPT-CL 2023-5535 from the ASKAP-EMU PILOT SURVEY

TL;DR

This paper reports the discovery of a radio relic and halo in a merging galaxy cluster at z=0.23 using ASKAP-EMU survey data, demonstrating the survey's effectiveness in detecting diffuse cluster emissions.

Contribution

First detection of a radio relic in the merging cluster SPT-CL 2023-5535 using ASKAP-EMU data, revealing complex radio features associated with cluster mergers.

Findings

Discovery of a 2 Mpc-scale radio halo aligned with intracluster gas.

Identification of a radio relic at the edge of the halo with spectral index -0.76.

Massive cluster with at least three subclusters from weak-lensing analysis.

Abstract

The ASKAP-EMU survey is a deep wide-field radio continuum survey designed to cover the entire southern sky and a significant fraction of the northern sky up to $+30^{\circ}$. Here, we report a discovery of a radio relic in the merging cluster SPT-CL 2023-5535 at z=0.23 from the ASKAP-EMU pilot 300 sq. deg survey (800-1088 MHz). The deep high-resolution data reveal a $\sim2$ Mpc-scale radio halo elongated in the east-west direction, coincident with the intracluster gas. The radio relic is located at the western edge of this radio halo stretched $\sim0.5$ Mpc in the north-south orientation. The integrated spectral index of the radio relic within the narrow bandwidth is $\alpha^{\scriptstyle \rm 1088~MHz}_{\scriptstyle \rm 800~MHz}=-0.76 \pm 0.06$. Our weak-lensing analysis shows that the system is massive ($M_{200}=1.04\pm0.36\times 10^{15} M_{\odot}$) and composed of at least three subclusters. We suggest a scenario, wherein the radio features arise from the collision between the eastern and middle subclusters. Our discovery illustrates the effectiveness of the ASKAP-EMU survey in detecting diffuse emissions in galaxy clusters and when completed, the survey will greatly increase the number of merging cluster detections with diffuse radio emissions.