A study of diffuse radio sources and X-ray emission in six massive clusters

TL;DR

This study investigates diffuse radio sources in six massive galaxy clusters at redshifts greater than 0.3, combining radio and X-ray observations to analyze their properties, detect emissions, and compare findings with existing models.

Contribution

It provides new radio observations of six high-redshift clusters, detecting diffuse emissions in four and setting upper limits for the others, including the discovery of an ultra-steep spectrum radio halo.

Findings

Diffuse radio emission detected in four clusters.

An ultra-steep spectrum radio halo found in MACSJ0417.5-1154.

Two clusters likely in the 'off-state' with radio powers below expected.

Abstract

The goal of the present study is to extend our current knowledge of the diffuse radio source (halo and relic) populations to $z$ $>$ 0.3. Here we report GMRT and EVLA radio observations of six galaxy clusters taken from the MAssive Cluster Survey (MACS) catalogue to detect diffuse radio emission. We used archival GMRT (150, 235 and 610 MHz) and EVLA (L band) data and made images at multiple radio frequencies of the following six clusters - MACSJ0417.5-1154, MACSJ1131.8-1955, MACSJ0308.9+2645, MACSJ2243.3-0935, MACSJ2228.5+2036 and MACSJ0358.8-2955. We detect diffuse radio emission (halo or relic or both) in the first four clusters. In the last two clusters we do not detect any diffuse radio emission but we put stringent upper-limits on their radio powers. We also use archival {\it Chandra} X-ray data to carry out morphology and substructure analysis of these clusters. We find that based on X-ray data, these MACS clusters are non-relaxed and show substructures in their temperature distribution. The radio powers of the first four MACS clusters are consistent with their expected values in the $L_{x}$--$P_{1.4GHz}$ plot. {However, we found ultra-steep spectrum radio halo in the MACSJ0417.5-1154 cluster whose rest-frame cut-off frequency is at $\sim$ 900 MHz}. The remaining two clusters whose radio powers are $\sim$ 11 times below the expected values are most likely to be in the `off-state' as has been postulated in some of the models of radio halo formation.