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.

Kinematic Structure of the Milky Way Galaxy, Near the Spiral Arm Tangents

“…They led to drawing the map of arm location (Fig. 1 in [1] for nearby arms; [14] for distant arms). A comparison between the locations of observed arm tangents and a fitted model of the locations of arm tangents showed a very good fit, as well as a comparison of the arm models from the parallax of radio masers and the arm models model from the arm tangents (Fig.…”

“…From published arm tracer separations and ages, the relative speed of the gas away from the arm shock front is estimated near 81 km/s (see [1] [7] [13]). In addition, a superposition of the known Galactic magnetic field can be made over the model spiral arm above, indicating that a counter-clockwise magnetic field covers the Sagittarius arm in Galactic Quadrant I and the Crux-Centaurus arm in Galactic Quadrant IV; the other arm segments and all other arms have a clockwise Galactic magnetic field [14].…”

Transport in Astrophysics: III. Diffusion from the Galactic Plane

“…Figure 12 reports a map of the theoretical synchrotron emission for a spiral galaxy as seen face on. The tendency to form an annulus, such as that reported in Figure 2 in [30], is due to the combination of the spiral structure with the diffusion of CRs.…”

“…Another interesting astrophysical feature is the annulus with enhanced synchrotron emission, whose distance from the galactic centre lies between 5.5 kpc and 7.6 kpc [30]. In Figure 14 we isolate a given region of simulated synchrotron emission.…”

“…A typical simulation of the galaxy's arms with the parameters as in Table 2 and radius of a cluster inversely proportional to its lifetime. A discussion of the location of the spiral arms and that of the peak of the total synchrotron emission can be found in [30].…”