Exploring the magnetic fields in local and distant galaxies
  (abridged) We investigate the possibility to recognize the magnetic field
structures in nearby galaxies and to test the cosmological evolution of their
large- and small-scale magnetic fields with the SKA and its precursors. We
estimate the required density of the background polarized sources detected with
the SKA for reliable reconstruction and reconstruction of magnetic field
structures in nearby spiral galaxies. The dynamo theory is applied to distant
galaxies to explore the evolution of magnetic fields in distant galaxies in the
context of a hierarchical dark matter cosmology. Under favorite conditions, a
\emph{recognition} of large-scale magnetic structures in local star-forming
disk galaxies (at a distance $\la 100$ Mpc) is possible from $\ga 10$ RMs
towards background polarized sources. Galaxies with strong turbulence or small
inclination need more polarized sources for a statistically reliable
recognition. A reliable \emph{reconstruction} of the field structure without
precognition needs at least 20 RM values on a cut along the projected minor
axis which translates to $\approx1200$ sources towards the galaxy. We
demonstrate that early regular fields are already in place at $z \sim 4$
(approximately 1.5 Gyr after the disk formation) in massive gas-rich galaxies
($>10^9$ M$_{\sun}$) which then evolve to Milky-Way type galaxies. Major and
minor mergers influence the star formation rate and geometry of the disk which
has an effect of shifting the generation of regular fields in disks to later
epochs. Predictions of the evolutionary model of regular fields, simulations of
the evolution of turbulent and large-scale regular fields, total and polarized
radio emission of disk galaxies, as well as future observational tests with the
SKA are discussed.
