An Improved Magnetic Map of the Milky Way, with the Circularly Orbiting Gas and Magnetic Field Lines Crossing the Dusty Stellar Spiral Arms

Abstract

Whether the Galactic magnetic field lines would or would not cross the spiral arms is a matter of debate. To reach the solution to this question, we first need rotation measure data over a wide range of longitudes, as well as a good distance estimate of the Sun's distance to the Galactic center (GC), and also the locations for the spiral arms (including observed tangents to the spiral arms). Six strong arguments that the magnetic field follows the gas in its circular orbit around the GC are put forward, allowing a consistent symbiosis between theory and observation. An analysis of a set of 554 pulsar rotation measure data currently available confirms and improves on an earlier finding that the Milky Way has a large-scale clockwise magnetic field, as seen from the north Galactic pole, except for a small anticlockwise ring near a radial distance of 5 kpc from the GC. Our pulsar results here broadly agree with the magnetic map of Brown and coworkers, which used rotation measure data from 149 quasars and galaxies in the radial range 12 kpc > rgal > 3.8 kpc (for R☉ = 7.6 kpc).