Magnetic field evolution in merging clusters of galaxies

We present initial results from the first three-dimensional numerical magne tohydrodynamical (MHD) simulations of magnetic held evolution in merging cl usters of galaxies. Within the framework of idealized initial conditions si milar to our previous work, we look at the gas dynamics and the magnetic fi eld evolution during a major merger event in order to examine the suggestio n that shocks and turbulence generated during a cluster/subcluster merger c an produce magnetic field amplification and relativistic particle accelerat ion 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 equ ations of ideal MHD, is evolved self-consistently within a changing gravita tional potential defined largely by the collisionless dark matter component represented by an N-body particle distribution. The MI-ID equations are so lved by the Eulerian, finite-difference code, ZEUS. The particles are evolv ed by a standard particle-mesh (PM) code. We find significant evolution of the magnetic held structure and strength during two distinct epochs of the merger evolution. In the first, the field becomes quite filamentary as a re sult of stretching and compression caused by shocks and bulk hows during in fall, but only minimal amplification occurs. In the second, amplification o f the held occurs more rapidly, particularly in localized regions, as the b ulk flow is replaced by turbulent motions (i.e., eddies). The total magneti c field energy is seen to increase by nearly a factor of 3 over that seen i n a nonmerging cluster. In localized regions (associated with high vorticit y), the magnetic energy can increase by a factor of 20 or more. A power spe ctrum analysis of the magnetic energy shows the amplification is largely co nfined to scales comparable to and smaller than the cluster cores, indicati ng that the core dimensions define the injection scale. Although the cluste r cores are numerically well-resolved, we cannot resolve the formation of e ddies on scales smaller than approximately half a core radius. Consequently , the held amplification noted here likely represents a lower limit. We dis cuss the effects of anomalous resistivity associated with the finite numeri cal resolution of our simulations on the observed field amplification.