Magnetic fields in nearby galaxies
  We describe a recent full-polarization radio continuum survey, performed
using the Westerbork Synthesis Radio Telescope (WSRT), of several nearby
galaxies in the Spitzer Infrared Nearby Galaxies Survey (SINGS) sample. The
WSRT-SINGS survey has been utilized to study the polarized emission and Faraday
rotation measures (RMs) in the targets, and reveals an important new
observational trend. The azimuthal distribution of polarized flux seems to be
intimately related to the kinematic orientation of galaxies, such that in
face-on galaxies the lowest level of polarized flux is detected along the
kinematic major axis. In highly inclined galaxies, the polarized flux is
minimized on both ends of the major axis, and peaks near the minor axis. Using
models of various three-dimensional magnetic field geometries, and including
the effects of turbulent depolarization in the midplane, we are able to
reproduce the qualitative distribution of polarized flux in the target
galaxies, its variation with inclination, and the distribution of RMs, thereby
constraining the global magnetic field structure in galaxies. Future radio
telescope facilities, now being planned and constructed, will have properties
making them extremely well-suited to perform vastly larger surveys of this
type, and are thereby poised to significantly increase our understanding of the
global structure of galactic magnetic fields. We discuss progress that can be
made using surveys which will be realized with these new facilities, focusing
in particular on the Aperture Tile in Focus (APERTIF) and Australian Square
Kilometre Array Pathfinder (ASKAP) telescopes, both based on Focal Plane Array
(FPA) designs, which are expected to be particularly useful for wide-field
polarization applications.
