Diffuse radio emission from non-Planck galaxy clusters in the LoTSS-DR2 fields

¹ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
e-mail: hoang@hs.uni-hamburg.de
² Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
³ Netherlands Institute for Radio Astronomy (ASTRON), PO Box 2 7990 AA Dwingeloo, The Netherlands
⁴ SRON Netherlands Institute for Space Research, Niels Bohrweg 4, 2333 CA Leiden, The Netherlands
⁵ Dipartimento di Fisica e Astronomia, Universitä di Bologna, via Gobetti 93/2, 40122 Bologna, Italy
⁶ INAF – Istituto di Radioastronomia di Bologna, Via Gobetti 101, 40129 Bologna, Italy
⁷ Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
⁸ INAF – IASF Milano, via A. Corti 12, 20133 Milano, Italy
⁹ Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo, Kashiwa, Chiba 277-8583, Japan

Received: 13 January 2022
Accepted: 31 May 2022

Abstract

Context. The presence of large-scale magnetic fields and ultra-relativistic electrons in the intra-cluster medium (ICM) is confirmed through the detection of diffuse radio synchrotron sources, so-called radio halos and relics. Due to their steep-spectrum nature, these sources are rarely detected at frequencies above a few gigahertz, especially in low-mass systems.

Aims. The aim of this study is to discover and characterise diffuse radio sources in low-mass galaxy clusters in order to understand their origin and their scaling with host cluster properties.

Methods. We searched for cluster-scale radio emission from low-mass galaxy clusters in the Low Frequency Array (LOFAR) Two-metre Sky Survey – Data Release 2 (LoTSS-DR2) fields. We made use of existing optical (Abell, DESI, WHL) and X-ray (comPRASS, MCXC) catalogues. The LoTSS-DR2 data were processed further to improve the quality of the images that are used to detect and characterise diffuse sources.

Results. We detect diffuse radio emission in 28 galaxy clusters. The numbers of confirmed (candidates) halos and relics are six (seven) and 10 (three), respectively. Among these, 11 halos and 10 relics, including candidates, are newly discovered by LOFAR. In addition to these, five diffuse sources are detected in tailed radio galaxies and are probably associated with mergers during the formation of the host clusters. We are unable to classify a further 13 diffuse sources. We compare our newly detected, diffuse sources to known sources by placing them on the scaling relation between the radio power and the mass of the host clusters.