CHANG-ES XXII: Coherent Magnetic Fields in the Halos of Spiral Galaxies
  Context. The magnetic field in spiral galaxies is known to have a large-scale
spiral structure along the galactic disk and is observed as X-shaped in the
halo of some galaxies. While the disk field can be well explained by dynamo
action, the 3-dimensional structure of the halo field and its physical nature
is still unclear.
  Aims. As first steps towards understanding the halo fields, we want to
clarify whether the observed X-shaped field is a wide-spread pattern in the
halos of spiral galaxies and whether these halo fields are just turbulent
fields ordered by compression or shear (anisotropic turbulent fields), or have
a large-scale regular structure.
  Methods. The analysis of the Faraday rotation in the halo is the tool to
discern anisotropic turbulent fields from large-scale magnetic fields. This,
however, has been challenging until recently because of the faint halo emission
in linear polarization. Our sensitive VLA broadband observations C-band and
L-band of 35 spiral galaxies seen edge-on (called CHANG-ES) allowed us to
perform RM-synthesis in their halos and to analyze the results. We further
accomplished a stacking of the observed polarization maps of 28 CHANG-ES
galaxies at C-band.
  Results. Though the stacked edge-on galaxies were of different Hubble types,
star formation and interaction activities, the stacked image clearly reveals an
X-shaped structure of the apparent magnetic field. We detected a large-scale
(coherent) halo field in all 16 galaxies that have extended polarized intensity
in their halos. We detected large-scale field reversals in all of their halos.
In six galaxies they are along lines about vertical to the galactic midplane
(vertical RMTL) with about 2 kpc separation. Only in NGC 3044 and possibly in
NGC 3448 we observed vertical giant magnetic ropes (GMRs) similar to those
detected recently in NGC 4631.
