Radio polarization data of spiral galaxies (see above observations of M 83) reveal large-scale
magnetic fields of turbulent origin. Contrary to stars, where
the dynamo mechanism acts in
the unobservable interior, a galactic dynamo can be observed
in detail. Our computations derive the
correct order of magnitude
of the magnetic field strength , i.e. a few µ Gauss
from very few assumptions. By tuning the unknown
correlation time of the interstellar turbulence it is also
possible to approach the observed magnetic geometry.
The vertical stratification of gaseous galactic disks is determined by
turbulent pressure. The interstellar turbulence is driven by
stellar winds as well
as by supernova explosions. The turbulence parameters computed
with this concept are used to
explain the large-scale magnetohydrodynamic structures in galaxies.
Due to the turbulence-induced viscosity the galactic gas is `spreading
out' in radial direction which influences the chemical evolution of
galactic disks.
In order to explain the observed properties of galactic magnetic fields we apply a new-developed 3D numerical code to an uniform external (primordial)
magnetic field subject to a complex flow pattern representing
the situation in a turbulent spiral galaxy.
No dynamo alpha-effect is assumed to exist
, but all the known turbulence effects such
as eddy diamagnetism and turbulent pumping are involved.
