Letter to the Editor

The MeerKAT massive distant clusters survey: A radio halo in a massive galaxy cluster at z = 1.23

¹ Astrophysics Research Centre, University of KwaZulu-Natal, Durban, 3696 South Africa
² School of Mathematics, Statistics & Computer Science, University of KwaZulu-Natal, Westville Campus, Durban, 4041 South Africa
³ Wits Centre for Astrophysics, School of Physics, University of the Witwatersrand, Private Bag 3, 2050 Johannesburg, South Africa
⁴ INAF-Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
⁵ Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, P.O. Box 94, Makhanda, 6140 South Africa
⁶ South African Radio Astronomy Observatory, 2 Fir Street, Black River Park, Observatory, Cape Town, 7925 South Africa
⁷ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
⁸ Department of Astronomy, Haverford College, Haverford, PA, 19041 USA
⁹ Instituto de Física, Pontificia Universidad Católica de Valparaíso, Casilla 4059, Valparaíso, Chile
¹⁰ Instituto de Astrofísica and Centro de AstroIngeniería, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
¹¹ NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD, 20771 USA

^⋆ Corresponding author: sikhosanas@ukzn.ac.za

Received: 12 December 2024
Accepted: 5 May 2025

Abstract

In the current theoretical paradigm, high-redshift radio haloes are expected to be scarce due to inverse Compton energy losses and redshift dimming, which cause them to be intrinsically faint. This low occurrence fraction is predicted by cosmic ray electron turbulent re-acceleration models. To date, only a handful of radio haloes have been detected at redshift z > 0.8. We report the MeerKAT detection of a radio halo hosted by the galaxy cluster ACT-CL J0329.2–2330 that has a mass of M_500c = 9.7^+1.7_−1.6 × 10¹⁴ M_⊙ and is at z = 1.23, making it the highest redshift halo detected thus far. Using L-band and UHF-band observations, we derive a radio halo spectral index of α^1.3 GHz_0.8GHz = 1.3 ± 0.4 and a radio power of P_1.4 GHz = (4.4 ± 1.5)×10²⁴ W Hz⁻¹ that is similar to the typical radio power of haloes hosted by low-redshift galaxy clusters. This result further confirms that there is rapid magnetic field amplification in galaxy clusters at high redshifts.