Can the large-scale magnetic field lines cross the spiral arms in our Milky Way galaxy?

Abstract

For the Sagittarius, Orion, and Perseus spiral arms, the pitch angle (i.e., deviation from a tangent parallel to a circular orbit around the center of the Galaxy) of the magnetic field lines differ from the pitch angle of the spiral arms. For the spiral arms, the pitch angle of the magnetic field lines can be measured independently from both quasars and galaxies as well as from pulsars, yielding a small (-6°) pitch angle, as predicted in the roughly circular oval gas streamline model of the density-wave theory. Meanwhile, the pitch angle of the spiral arms can be measured independently from both the O type stars and from the H II regions, yielding a large (-18°) pitch angle, also as predicted in the density-wave theory. Thus for these arms, the magnetic field lines cross the spiral arms, to leave them outwardly at a sizable mean angle (+12°).