Magnetic flux density from the relative circular motion of stars and   partially ionized gas in the Galaxy mid-plane vicinity
  Observations suggest a slower stellar rotation relative to gas rotation in the outer part of the Milky Way Galaxy. This difference could be attributed to an interaction with the interstellar magnetic field. In a simple model, fields of order 10 micro Gauss are then required, consistently with the observed values. This coincidence suggests a tool for estimating magnetic fields in spiral galaxies. A North-South asymmetry in the rotation of gas in the Galaxy could be of magnetic origin too. 
Joanna Ja{\l}ocha, {\L}ukasz Bratek, Jan P\k{e}kala, Szymon Sikora,   Marek Kutschera
astro-ph.GA