Discovery of a Radio Relic in the Massive Merging Cluster SPT-CL J2023-5535 from the ASKAP-EMU Pilot Survey

September 2020 • 2020ApJ...900..127H

Authors • HyeongHan, Kim • Jee, M. James • Rudnick, Lawrence • Parkinson, David • Finner, Kyle • Yoon, Mijin • Lee, Wonki • Brunetti, Gianfranco • Brüggen, Marcus • Collier, Jordan D. • Hopkins, Andrew M. • Michałowski, Michał J. • Norris, Ray P. • Riseley, Chris

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°. Here, we report a discovery of a radio relic in the merging cluster SPT-CL J2023-5535 at z = 0.23 from the ASKAP-EMU pilot 300 square degree survey (800-1088 MHz). The deep high-resolution data reveal a ∼2 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 ∼0.5 Mpc in the north-south orientation. The integrated spectral index of the radio relic within the narrow bandwidth is ${\alpha }_{800\,\mathrm{MHz}}^{1088\,\mathrm{MHz}}=-0.76\pm 0.06$ . Our weak-lensing analysis shows that the system is massive ( ${M}_{200}=1.04\pm 0.36\times {10}^{15}\,{M}_{\odot }$ ) 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.

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Kyle Finner

Postdoctoral Research Associate