An Objective Survey of Mpc-Scale Radio Emission in 0.03<z<0.3 Bright X-ray Clusters

TL;DR

This study provides the first comprehensive census of Mpc-scale radio emission in bright X-ray clusters within 0.03<z<0.3, revealing correlations with X-ray luminosity and new diffuse radio sources, advancing understanding of cluster radio phenomena.

Contribution

It offers the first quantitative survey including control fields and upper limits, confirming detection trends and discussing selection effects in radio-X-ray correlations.

Findings

Approximately 30% of clusters show diffuse radio emission.

Higher detection rates at X-ray luminosities above 10^45 erg/s.

Discovery of new diffuse radio sources, including relics and potential halos.

Abstract

We have performed the the first census of Mpc-scale radio emission to include control fields and quantifiable upper limits for bright X-ray clusters in the range 0.03<z<0.3 . Through reprocessing radio images from the WENSS survey, we detect diffuse emission from approximately 30% of the sample. We find a correlation similar to the well-studied relationship between radio halo and X-ray luminosities of the host cluster, but also find that large scale radio galaxy detections follow a similar trend to that for radio halos. With this quantitative study, we thus confirm the upper envelope to the radio luminosities for X-ray selected clusters, and the higher detection rates for diffuse radio emission (including halos, relics and radio galaxies) at X-ray luminosities above approximately 10**45 erg/s. We can neither confirm nor refute the claims for a tight correlation between these radio halo and X-ray luminosities, i.e. whether the halo luminosity function of X-ray clusters is bimodal (having high/on and low/off states), or whether the radio luminosity can take on a wide range of values up to a maximum at each cluster X-ray luminosity. The resolution of this issue may provide a unique diagnostic for the timescales over which relativistic particles can be accelerated following cluster mergers. We discuss several important selection effects on radio vs. X-ray luminosity correlations, including surface brightness thresholds and non-X-ray-selected diffuse radio sources. We also report several new detections of diffuse emission, including a Mpc-scale relic in RXJ1053.7+5450, a possible halo/relic combination in Abell 2061, a serendipitous diffuse X-ray source associated with poor clusters in the Abell 781 field, and confirmation of very weak diffuse emission patches outside of Abell~2255.