Global MHD simulations of galactic gas disks

Abstract

We present the results of global three-dimensional magnetohydro-dynamic simulations of galactic gas disks. Numerical results indicate that magneto-rotational instability amplifies magnetic fields. The growth of magnetic fields saturates when B ∼ 1.5µG. This saturation level is almost independent of the strength of the initial magnetic field. The magnetic loops buoyantly rising from the disk supply azimuthal magnetic flux to the halo. We found that mean azimuthal magnetic fields inside the disk reverse their direction with interval about 1Gyr. The field reversal takes place following the buoyant escape of azimuthal magnetic flux amplified in the disk. The quasi-periodic reversals of azimuthal magnetic fields create a magnetically striped halo, in which azimuthal magnetic fields reverse their direction with height.