Numerical simulation of large-scale magnetic-field evolution in spiral galaxies

Abstract

The evolution of large-scale magnetic fields in disk galaxies is investigated numerically. The gasdynamical simulations in a disk perturbed by spiral or bar potential are incorporated into the kinematic calculations of induction equations to elucidate the effects of non-axisymmetric disk structure on magnetic fields. The effects of interstellar turbulence are given as the turbulent diffusion of magnetic fields. The usually adopted dynamo mechanism of alpha-effect is not considered in our computations, because it is not obvious about the actual existence of the effect in a galaxy. Our principal concern is to clear how observationally and theoretically well-established gas flow affects the magnetic-field structure and evolution, without putting a lot of artificial parameters in the model. We have found that the density-wave streaming motion of gas has a significant influence on the distribution of magnetic fields: the lines of force are well aligned with spiral arms due to the compressional and additional shearing flow of gas in these regions.