Rotation Measures of Radio Sources in Hot Galaxy Clusters

TL;DR

This study investigates the Faraday rotation measures of radio galaxies in hot galaxy clusters to explore the relationship between magnetic field strength and intracluster gas temperature, revealing small-scale magnetic fluctuations and weak temperature dependence.

Contribution

The paper provides detailed RM maps of radio galaxies in hot clusters and compares these with cooler clusters, highlighting magnetic field fluctuations and the weak correlation with gas temperature.

Findings

RM structures are patchy with kpc-scale substructures.

Higher temperature clusters show greater RM dispersion.

No strong link found between magnetic field strength and gas temperature.

Abstract

The goal of this work is to investigate the Faraday rotation measure (RM) of radio galaxies in hot galaxy clusters in order to establish a possible connection between the magnetic field strength and the gas temperature of the intracluster medium. We performed Very Large Array observations at 3.6 cm and 6 cm of two radio galaxies located in A401 and Ophiuchus, a radio galaxy in A2142, and a radio galaxy located in the background of A2065. All these galaxy clusters are characterized by high temperatures. We obtained detailed RM images at an angular resolution of 3'' for most of the observed radio galaxies. The RM images are patchy and reveal fine substructures of a few kpc in size. Under the assumption that the radio galaxies themselves have no effect on the measured RMs, these structures indicate that the intracluster magnetic fields fluctuate down to such small scales. These new data are compared with RM information present in the literature for cooler galaxy clusters. For a fixed projected distance from the cluster center, clusters with higher temperature show a higher dispersion of the RM distributions (sigmaRM), mostly because of the higher gas density in these clusters. Although the previously known relation between the clusters X-ray surface brightness (Sx) at the radio galaxy location and sigmaRM is confirmed, a possible connection between the sigmaRM-Sx relation and the cluster temperature, if present, is very weak. Therefore, in view of the current data, it is impossible to establish a strict link between the magnetic field strength and the gas temperature of the intracluster medium.