Diffuse radio sources in a statistically complete sample of high-redshift galaxy clusters

¹ Dipartimento di Fisica e Astronomia, University of Bologna, Via Gobetti 93/2, 4019 Bologna, Italy
e-mail: ggiovann@ira.inaf.it
² INAF – Istituto di Radioastronomia, Via P. Gobetti 101, 40129 Bologna, Italy
³ Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
⁴ Dipartimento di Fisica, Università di Trieste, Via A. Valerio 2, 34127 Trieste, Italy
⁵ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius, CA, Italy
⁶ Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131, USA

Received: 25 April 2020
Accepted: 12 June 2020

Abstract

Aims. Non-thermal properties of galaxy clusters have been studied using detailed and deep radio images in comparison with X-ray data. While much progress has been made in this area, most of the studied clusters are at a relatively low redshift (z <  0.3). Here we investigate the evolutionary properties of the non-thermal cluster emission using two statistically complete samples at z >  0.3.

Methods. We obtained short JVLA observations at the L-band of the statistically complete sample of very X-ray luminous clusters from the Massive Cluster Survey (MACS), namely 34 clusters in the redshift range of 0.3–0.5 and with nominal X-ray fluxes in excess of 2 × 10⁻¹² erg s⁻¹ cm⁻² (0.1–2.4 keV) in the ROSAT Bright Source Catalogue. We add to this list the complete sample of the 12 most distant MACS clusters (z >  0.5).

Results. Most clusters show evidence of emission in the radio regime. We present the radio properties of all clusters in our sample and show images of newly detected diffuse sources. A radio halo is detected in 19 clusters and five clusters contain a relic source. Most of the brightest cluster galaxies (BCG) in relaxed clusters show radio emission with powers typical of FRII radio galaxies and some are surrounded by a radio mini-halo.

Conclusions. The high frequency of radio emission from the BCG in relaxed clusters suggests that BCG feedback mechanisms are already in place at z ∼ 0.6. The properties of radio halos and the small number of detected relics suggest redshift evolution in the properties of diffuse sources. The radio power (and size) of radio halos could be related to the number of past merger events in the history of the system. In this scenario, the presence of a giant and high-power radio halo is indicative of an evolved system with a large number of past major mergers, whereas small low-power halos are found in less evolved clusters.