A Three-dimensional Model for the Reversal in the Local Large-scale Interstellar Magnetic Field

Abstract We probe the three-dimensional geometry of the large-scale Galactic magnetic field within 1 kpc of the Sun using the Dominion Radio Astrophysical Observatory Global Magneto-Ionic Medium Survey (GMIMS) of the Northern Sky (DRAGONS). DRAGONS is a new full polarization survey of the northern sky from 350 to 1030 MHz covering decl. of –20° &lt; δ &lt; 90° and a component of GMIMS. The first moment of the Faraday depth (FD) spectra produced from DRAGONS above 500 MHz reveals large-angular-scale FD structures with signs that alternate only once in the southern Galactic hemisphere and twice in the northern hemisphere, patterns shared by other Faraday rotation datasets. DRAGONS is the first survey to achieve high FD resolution while maintaining sensitivity to broad FD structures, enabling the first use of Galactic longitude–FD plots. These plots reveal Faraday-complex structures across the sky, indicating a slablike scenario in which emission and Faraday rotation are mixed. This complexity is overlaid on the same large-scale FD patterns that appear in the first moment map. We model these patterns as a magnetic reversal slicing through the disk on a diagonal and passing above the Sun in Galactic coordinates. We describe this reversal as a plane with a normal vector parallel to the line directed along ( ℓ , b ) = (168 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 5, −60°) and estimate its distance to be between 0.25 and 0.55 kpc. Our results show that much of the observed Faraday sky may be dominated by the local magnetic field configuration.