CHANG-ES XIII: Transport processes and the magnetic fields of NGC 4666 -
  indication of a reversing disk magnetic field
  We analyze the magnetic field geometry and the transport processes of the
cosmic rays of the edge-on spiral starburst galaxy NGC 4666 from CHANG-ES radio
continuum data in two frequencies; 6 GHz (C-band) and 1.5 GHz (L-band).
Supplementary X-ray data are used to investigate the hot gas in NGC 4666. We
determine the radio scale heights of total power emission at both frequencies
for this galaxy. We show the magnetic field orientations derived from the
polarization data. Using rotation measure (RM) synthesis we further study the
behavior of the RM values along the disk in C-band to investigate the
large-scale magnetic-field pattern. We use the revised equipartition formula to
calculate a map of the magnetic field strength. Furthermore, we model the
processes of cosmic-ray transport into the halo with the 1D SPINNAKER model.
The extended radio halo of NGC 4666 is box-shaped and is probably produced by
the previously observed supernova-driven superwind. This is supported by our
finding of an advective cosmic-ray transport such as that expected for a
galactic wind. The scaleheight analysis revealed an asymmetric halo above and
below the disk as well as between the two sides of the major axis. A central
point source as well as a bubble structure is seen in the radio data for the
first time. Our X-ray data show a box-shaped hot halo around NGC 4666 and
furthermore confirm the AGN nature of the central source. NGC 4666 has a
large-scale X-shaped magnetic field in the halo, as has been observed in other
edge-on galaxies. The analysis furthermore revealed that the disk of NGC 4666
shows hints of field reversals along its radius, which is the first detection
of this phenomenon in an external galaxy.
