Originally Posted by Markarov & Murphy

The most unexpected and unexplained term within the Ogorodnikov-Milne model is the first-degree magnetic harmonic representing a rigid rotation of the stellar field about the axis −Y pointing opposite to the direction of rotation. This harmonic comes out with a statistically robust coefficient 6.2±0.9 kms−1 kpc−1, and is also present in the velocity field of more distant stars. The ensuing upward vertical motion of stars in the general direction of the Galactic center and the downward motion in the anticenter direction are opposite to the vector field expected from the stationary Galactic warp model.

Originally Posted by Beck

Radio polarization observations revealed magnetic fields of considerable strength in all galaxies containing a significant amount of cold gas (see Beck 2005 for a review)...

NGC 6946 is bright in all spectral ranges and hence an ideal laboratory to test the interaction between the components of the interstellar medium...

The combined 6.2 cm polarization map by Beck & Hoernes (1996) revealed two surprisingly symmetric “magnetic spiral arms” located between the optical spiral arms. After subtraction of the diffuse unpolarized radio background the degree of polarization is 30–60%. This means that the field in themagnetic arms is almost perfectly aligned, parallel to the adjacent spiral arms. The symmetry and alignment of the magnetic arms indicated that a new kind of physical phenomenon was discovered, with possibly major consequences for our understanding of galactic magnetic fields...

After the discovery of the magnetic arms in NGC 6946, several authors presented dynamo models with generation of magnetic arms...

In this paper new multi-wavelength radio observations of NGC 6946 which were obtained during the last years are presented and discussed. The two main magnetic arms are confirmed at all wavelengths, but more magnetic arms exist. The almost perfect alignment of the magnetic field vectors along the arm structure suggests close interaction between the field and the gas flow.

Originally Posted by Beck

In the Milky Way, Faraday rotation data from pulsars indicate multiple large-scale field reversals (Han et al. 2006). Nothing similar has been observed in any external galaxy so far. Although Faraday rotation data in galaxies like NGC 6946 are line-of-sight integrals, large-scale field reversals would be evident from the existing data. Furthermore, the general concentration of coherent fields in interarm regions, like in many spiral galaxies, was not found in the Milky Way. Either our Galaxy is special, or the data are not yet sufficient to trace the large-scale Galactic field.

Originally Posted by Han

Magnetic fields have been observed on all scales in our Galaxy, from AU to kpc. With pulsar dispersion measures and rotation measures, we can directly measure the magnetic fields in a very large region of the Galactic disk. The results show that the large-scale magnetic fields are aligned with the spiral arms but reverse their directions many times from the inner-most arm (Norma) to the outer arm (Perseus). The Zeeman splitting measurements of masers in HII regions or star-formation regions not only show the structured fields inside clouds, but also have a clear pattern in the global Galactic distribution of all measured clouds which indicates the possible connection of the large-scale and small-scale magnetic fields.