Correlation of the magnetic field and the intra-cluster gas density in galaxy clusters

¹ Max-Planck-Institut für Astrophysik, PO Box 1317, 85741 Garching, Germany
² Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Birkenhead CH41 1LD, UK
³ Dipartimento di Astronomia, Univ. Bologna, Via Ranzani 1, 40127 Bologna, Italy
⁴ Istituto di Radioastronomia CNR, Via P. Gobetti, 101 40129 Bologna, Italy

Corresponding author: K. Dolag, kdolag@mpa-garching.mpg.de

Received: 1 August 2001
Accepted: 28 August 2001

Abstract

We present a correlation between X-ray surface brightness and Faraday rotation measure in galaxy clusters, both, from radio and X-ray observations as well as from modeling of the intra-cluster medium. The observed correlation rules out a magnetic field of constant strength throughout the cluster. Cosmological, magneto-hydrodynamic simulations of galaxy clusters are used to show that for a magnetic field of cosmic origin this correlation is expected and excellently reproduces the observations showing that the rms scatter of the Faraday rotation increases linearly with the X-ray surface brightness. From the correlation between the observable quantities, rotation measure and X-ray surface brightness, we infer a relation between the physical quantities: magnetic field and gas density. For the best available observations, those of A119, we find .