The effect of magnetic fields on the mass determination of clusters of galaxies

We test the effects of magnetic fields on the mass determination of galaxy clusters with the X-ray method. As this method takes into account only ther mal pressure, additional non-thermal pressure support, e.g. caused by a mag netic field, can result in an underestimation of the mass. SPH models of ga laxy clusters including magnetic fields of various strengths in two differe nt cosmologies are used for the test. We compare the true mass of the model clusters with the mass determined from simulated X-ray images of the same models. The effect of the magnetic field on the mass in relaxed clusters is found to be negligible compared to other uncertainties, even at small radi i, where the strongest effects are expected. However in one model, in which the cluster is in the process of merging, we find an effect of up to a fac tor of 2 caused by the magnetic field. In relaxed clusters the mass estimat e, averaged over many models, is at most 15% smaller in models with relativ ely high magnetic field of 2 muG compared to models without a magnetic fiel d with a small dependence on the cosmology chosen. Therefore we conclude th at the presence of a magnetic field cannot be responsible for the discrepan cies of a factor of 2-3 found between X-ray and lensing mass in the central regions of relaxed clusters.