Discovery of a
z
∼ 0.8 ultra steep spectrum radio halo in the MeerKAT-South Pole Telescope Survey
Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 545:1 (2025) staf2022
Authors:
Isaac S Magolego, Roger P Deane, Kshitij Thorat, Ian Heywood, William Rasakanya, Manuel Aravena, Lindsey E Bleem, Maria G Campitiello, Kedar A Phadke, Justin Spilker, Joaquin D Vieira, Dazhi Zhou, Bradford A Benson, Scott Chapman, Ana Posses, Tim Schrabback, Antony Stark, David Vizgan
Abstract:
ABSTRACT
Radio haloes are diffuse synchrotron sources that trace the turbulent intracluster medium (ICM) of galaxy clusters. However, their origin remains unknown. Two main formation models have been proposed: the hadronic model, in which relativistic electrons are continuously injected by cosmic-ray protons; and the leptonic turbulent re-acceleration model, where cluster mergers re-energize electrons in situ. A key discriminant between the two models would be the existence of ultra-steep spectrum radio haloes (USSRHs), which can only be produced through turbulent re-acceleration. Here, we report the discovery of an USSRH in the galaxy cluster SPT-CLJ2337–5942 at redshift $z = 0.78$ in the MeerKAT-South Pole Telescope 100 deg$^2$ UHF (0.58–1.09 GHz) survey. This discovery is noteworthy for two primary reasons: it is the highest redshift USSRH system to date; and the close correspondence of the radio emission with the thermal ICM as traced by Chandra X-ray observations, further supporting the leptonic re-acceleration model. The halo is underluminous for its mass, consistent with a minor merger origin, which produces steep-spectrum, lower luminosity haloes. This result demonstrates the power of wide-field, high-fidelity, low-frequency ($\lesssim 1$ GHz) surveys like the MeerKAT-SPT 100 deg$^2$ programme to probe the origin and evolution of radio haloes over cosmic time, ahead of the Square Kilometre Array.
