Structure, dynamical impact and origin of magnetic fields in nearby
  galaxies in the SKA era
  Magnetic fields are an important ingredient of the interstellar medium (ISM).
Besides their importance for star formation, they govern the transport of
cosmic rays, relevant to the launch and regulation of galactic outflows and
winds, which in turn are pivotal in shaping the structure of halo magnetic
fields. Mapping the small-scale structure of interstellar magnetic fields in
many nearby galaxies is crucial to understand the interaction between gas and
magnetic fields, in particular how gas flows are affected. Elucidation of the
magnetic role in, e.g., triggering star formation, forming and stabilising
spiral arms, driving outflows, gas heating by reconnection and magnetising the
intergalactic medium has the potential to revolutionise our physical picture of
the ISM and galaxy evolution in general. Radio polarisation observations in the
very nearest galaxies at high frequencies (>= 3 GHz) and with high spatial
resolution (<= 5") hold the key here. The galaxy survey with SKA1 that we
propose will also be a major step to understand the galactic dynamo, which is
important for models of galaxy evolution and for astrophysical
magnetohydrodynamics in general. Field amplification by turbulent gas motions,
which is crucial for efficient dynamo action, has been investigated so far only
in simulations, while compelling evidence of turbulent fields from observations
is still lacking.
