Magnetic field structure and halo in NGC 4631
  In order to clarify whether NGC 4631 has a unique magnetic field
configuration in the central region along its disk, we present high-resolution
Faraday-corrected polarization data. Radio continuum observations of NGC 4631
at 4.85 GHz were performed with the VLA. In addition, observations were made
with the Effelsberg telescope at 4.85 GHz and at 8.35 GHz. These were analyzed
together with archival VLA-data at 8.35 GHz. The vertical scale heights in NGC
4631 vary significantly in different regions within the galaxy and their mean
values at 4.85 GHz are with 2.3 kpc (370 pc) for the thick (thin) disk higher
than the mean values found so far in six other edge-on spiral galaxies. This
may originate in the tidal interaction of NGC 4631 with its neighbouring
galaxies. The total field strengths in the halo are of the order of the total
magnetic field strength in the disk, whereas the ordered field strengths in the
halo seem to be higher than the value in the disk. The derived distribution of
rotation measures implies that NGC 4631 has a large-scale regular magnetic
field configuration. Despite the strong Faraday depolarization along the
galactic plane and the strong beam depolarization in the transition zone
between the disk and halo, our research strongly indicates that the magnetic
field orientation along the central 5-7 kpc of the disk is also plane-parallel.
Therefore, we claim that NGC 4631 also has a magnetic field structure
plane-parallel along its entire disk.
