Diffuse radio emission from galaxy clusters in the LOFAR Two-metre Sky Survey Deep Fields

¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
e-mail: osinga@strw.leidenuniv.nl
² Istituto Nazionale di Astrofisica, Istituto di Radioastronomia Via P Gobetti 101, 40129 Bologna, Italy
³ Hamburg Observatory, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
⁴ ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁵ DIFA – Universitá di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy
⁶ SUPA, Institute for Astronomy, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
⁷ Italian ALMA Regional Centre, Via Gobetti 101, 40129 Bologna, Italy
⁸ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁹ INAF – IASF Milano, Via A. Corti 12, 20133 Milano, Italy
¹⁰ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
¹¹ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
¹² Department of Physics & Electronics, Rhodes University, PO Box 94, Grahamstown 6140, South Africa

Received: 31 July 2020
Accepted: 26 January 2021

Abstract

Low-frequency radio observations are revealing an increasing number of diffuse synchrotron sources from galaxy clusters, primarily in the form of radio halos or radio relics. The existence of this diffuse synchrotron emission indicates the presence of relativistic particles and magnetic fields. It is still an open question as to exactly what mechanisms are responsible for the population of relativistic electrons driving this synchrotron emission. The LOFAR Two-metre Sky Survey Deep Fields offer a unique view of this problem. Reaching noise levels below 30 μJy beam⁻¹, these are the deepest images made at the low frequency of 144 MHz. This paper presents a search for diffuse emission in galaxy clusters in the first data release of the LOFAR Deep Fields. We detect a new high-redshift radio halo with a flux density of 8.9 ± 1.0 mJy and corresponding luminosity of P_144MHz = (3.6 ± 0.6) × 10²⁵ W Hz⁻¹ in an X-ray detected cluster at z = 0.77 with a mass estimate of M₅₀₀ = 3.3_−1.7^+1.1 × 10¹⁴ M_⊙. Deep upper limits are placed on clusters with non-detections. We compare the results to the correlation between halo luminosity and cluster mass derived for radio halos found in the literature. This study is one of a few to find diffuse emission in low mass (M₅₀₀ < 5 × 10¹⁴ M_⊙) systems and shows that deep low-frequency observations of galaxy clusters are fundamental for opening up a new part of parameter space in the study of non-thermal phenomena in galaxy clusters.