Topological evolution of Parker-unstable galactic magnetic fields under the influence of Coriolis force and magnetic reconnection

Abstract

We investigate the influence of the Coriolis force and magnetic reconnection on the evolution of the Parker instability in galactic disks. We apply a model of a local gas cube, permeated by an azimuthal large-scale magnetic field and solve numerically resistive 3D MHD equations including the contribution of the Coriolis force. We introduce a current-dependent resistivity which switches the magnetic reconnection above a certain critical current density. We study the evolution of the magnetic field topology and the formation of large-scale poloidal magnetic fields from the initial azimuthal field. Our simulations demonstrate that the Parker instability leads to the formation of helically twisted magnetic flux tubes which are then agglomerated by magnetic reconnection forming, a significant poloidal magnetic field component on the scale of the whole cube. Such an evolution represents a kind of fast dynamo process as proposed by Parker (1992, ApJ 401, 137).