Superposing the Magnetic Spiral Structure of the Milky Way, on the Stellar Spiral Arms—Matching the Unique Galactic Magnetic Field Reversal Zone with Two Galactic Spiral Arm Segments

Abstract

To pinpoint the peak location of the synchrotron total intensity emission in a spiral arm, we use a map of the spiralarm locations (from the observed arm tangent). Thus in a typical spiral arm in Galactic Quadrant I, we find the peak of the synchrotron radiation to be located about 220 ± 40 pc away from the inner arm edge (hot dust lane) inside the spiral arm. While most of the galactic disk has a clockwise large-scale magnetic field, we make a statistical analysis to delimitate more precisely the smaller reverse annulus with a counterclockwise galactic magnetic field. We find an annulus width of 2.1 ± 0.3 kpc (measured along the Galactic radius), located from 5.5 to 7.6 kpc from the Galactic Center). The annulus does not overlay with a single spiral arm—it encompasses segments of two different spiral arms. Using a recent delineation of the position of spiral arms, the field-reversed annulus is seen to encompass the Crux-Centaurus arm (in Galactic Quadrant IV) and the Sagittarius arm (in Galactic Quadrant I). Thus the full Sagittarius-Carina arm is composed of: 1) a Sagittarius arm (in Galactic quadrant I) with a counterclockwise magnetic field, and 2) a Carina arm (in Galactic Quadrant IV) with a clockwise magnetic field. Also the full Scutum-Crux-Centaurus arm is composed of: 1) a Scutum arm (in Galactic Quadrant I) with a clockwise magnetic field, and 2) a Crux-Centaurus arm (in Galactic Quadrant IV) with a counterclockwise magnetic field. Arm segments do not all have the same magnetic field direction. For completeness, we display 6 known magnetised advancing supershells around the Sun (within 400 pc), pushing out the interstellar magnetic field.