Global enhancement and structure formation of the magnetic field in
  spiral galaxies
  We study numerically large-scale magnetic field evolution and its enhancement
in gaseous disks of spiral galaxies. We consider a set of models with the
various spiral pattern parameters and the initial magnetic field strength with
taking into account gas self-gravity and cooling/heating. In agreement with
previous studies, we find out that galactic magnetic field is mostly aligned
with gaseous structures, however small-scale gaseous structures (spurs and
clumps) are more chaotic than the magnetic field structure. In spiral arms
magnetic field strongly coexists with the gas distribution, in the inter-arm
region we see filamentary magnetic field structure. Simulations reveal the
presence of the small-scale irregularities of the magnetic field as well as the
reversal of magnetic field at the outer edge of the large-scale spurs. We
provide evidences that the magnetic field in the spiral arms has a stronger
mean-field component, and there is a clear inverse correlation between gas
density and plasma-beta parameter, compared to the rest of the disk with a more
turbulent component of the field and an absence of correlation between gas
density and plasma-beta. We show the mean field growth up to 3-10$\mu G$ in the
cold gas during several rotation periods (500-800 Myr), whereas ratio between
azimuthal and radial field is equal to 4/1. Mean field strength increases by a
factor of 1.5-2.5 for models with various spiral pattern parameters. Random
magnetic field component can reach up to 25 % from the total strength. By
making an analysis of the time-depended evolution of radial Poynting flux we
point out that the magnetic field strength is enhanced stronger at the galactic
outskirts which is due to the radial transfer of magnetic energy by the spiral
arms pushing the magnetic field outward. Our results also support the presence
of sufficient conditions for development of MRI at distances >11 kpc.
