Rotation measures of radio sources in hot galaxy clusters^⋆

¹ INAF - Osservatorio Astronomico di Cagliari, Loc. Poggio dei Pini, Strada 54, 09012 Capoterra (CA), Italy
e-mail: fgovoni@ca.astro.it
² Max-Planck-Institut für Astrophysik, Garching, Germany
³ INAF - Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
⁴ Institut für Astrophysik, Leopold-Franzens Universität Innsbruck, Technikerstrae 25, 6020 Innsbruck, Austria
⁵ Dipartimento di Astronomia, Univ. di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁶ Fundación Galileo Galilei - INAF, Rambla José Ana Fernández Perez 7, 38712 Breña Baja (La Palma), Canary Islands, Spain
⁷ Dipartimento di Astronomia, Università degli Studi di Trieste, via Tiepolo 11, 34143 Trieste, Italy
⁸ Dipartimento di Fisica, Università degli Studi di Cagliari, Cittadella Universitaria, 09042 Monserrato (CA), Italy

Received: 13 November 2009
Accepted: 14 July 2010

Abstract

Aims. 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.

Methods. 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.

Results. 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 (σ_RM), mostly because of the higher gas density in these clusters. Although the previously known relation between the clusters X-ray surface brightness (S_X) at the radio galaxy location and σ_RM is confirmed, a possible connection between the σ_RM − S_X 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.