Magnetic field evolution in dwarf and Magellanic-type galaxies
  Low-mass galaxies radio observations show in many cases surprisingly high
levels of magnetic field. The mass and kinematics of such objects do not favour
the development of effective large-scale dynamo action. We attempted to check
if the cosmic-ray-driven dynamo can be responsible for measured magnetization
in this class of poorly investigated objects. We investigated how starburst
events on the whole, as well as when part of the galactic disk, influence the
magnetic field evolution. We created a model of a dwarf/Magellanic-type galaxy
described by gravitational potential constituted from two components: the stars
and the dark-matter halo. The model is evolved by solving a three-dimensional
(3D) magnetohydrodynamic equation with an additional cosmic-ray component,
which is approximated as a fluid. The turbulence is generated in the system via
supernova explosions manifested by the injection of cosmic-rays.The
cosmic-ray-driven dynamo works efficiently enough to amplify the magnetic field
even in low-mass dwarf/Magellanic-type galaxies. The $e$-folding times of
magnetic energy growth are 0.50 and 0.25 Gyr for the slow (50 km/s) and fast
(100 km/s) rotators, respectively. The amplification is being suppressed as the
system reaches the equipartition level between kinetic, magnetic, and
cosmic-ray energies. An episode of star formation burst amplifies the magnetic
field but only for a short time while increased star formation activity holds.
We find that a substantial amount of gas is expelled from the galactic disk,
and that the starburst events increase the efficiency of this process.
