Contribution of the Cluster Diffuse Magnetic Field to the Support of X-Ray Gas and Mass Distributions in Clusters of Galaxies

We study the cluster mass distributions that are derived from observations of the X-ray gas, Faraday rotation, and gravitational arc images. The Faraday rotation measure is inferred to be that resulting from the magnetic field, derived as the difference between the gas pressure gradient (determined from the X-ray images) and the gravitational potential (determined from the arcs). It is found that the magnetic field cannot affect the gas distribution if the gas density and the rotation measure of the cluster are not very different from those of the Coma Cluster. We estimate the rotation measure in A2218, requiring that the mass distribution be consistent with observation of the giant arc image and the X-ray surface brightness. We compare the result with observed values in nearby clusters. In conclusion we find that the magnetic pressure can contribute substantially to supporting the gas against the gravity produced by the mass distribution, which can form the giant arc.