MAGNETIC FIELD EVOLUTION IN MERGING CLUSTERS OF GALAXIES

摘要

We present initial results from the first three-dimensional numerical magnetohydrodynamical (MHD) simulations of magnetic field evolution in merging clusters of galaxies. Within the framework of idealized initial conditions similar to our previous work, we look at the gas dynamics and the magnetic field evol- ution during a major merger event in order to examine the suggestion that shocks and turbulence gener- ated during a cluster/subcluster merger can produce magnetic field amplification and relativistic particle acceleration and, as such, may play a role in the formation and evolution of cluster-wide radio halos. The intracluster medium (ICM), as represented by the equations of ideal MHD, is evolved self consistently within a changing gravitational potential defined largely by the collisionless dark matter component represented by an N-body particle distribution. The MHD equations are solved by the Eulerian, finite-difference code, ZEUS. The particles are evolved by a standard particle-mesh (PM) code. We find significant evolution of the magnetic field structure and strength during two distinct epochs of the merger evolution, In the first, the field becomes quite filamentary as a result of stretching and com- pression caused by shocks and bulk flows during infall, but only minimal amplification occurs. In the second, amplification of the field occurs more rapidly, particularly in localized regions, as the bulk flow is replaced by turbulent motions (i.e., eddies). The total magnetic field energy is seen to increase by nearly a factor of 3 over that seen in a nonmerging cl