Modeling the Magnetic Field in the Galactic Disk Using New Rotation Measure Observations From the Very Large Array

We have determined 194 Faraday rotation measures (RMs) of polarized extragalactic radio sources using , multi-channel polarization observations at frequencies around 1.4 GHz from the Very Large Array (VLA) in the Galactic plane at 17◦ ≤ l ≤ 63◦ and 205◦ ≤ l ≤ 253◦. This catalog fills in gaps in the RM coverage of the plane between the Canadian Galactic Plane Survey and Southern Galactic Plane Survey. Using this we have tested the validity of recently-proposed axisymmetric and bisymmetric models of the largescale (or regular) Galactic magnetic field, and found that of the existing models we tested, an axisymmetric model with reversals occurring in rings (as opposed to along spiral arms) best matched our observations. on this, we have performed our own modeling, using RMs from both extragalactic sources and pulsars. developing independent models for the magnetic field in the outer and inner Galaxy, we conclude that in the Galaxy, the magnetic field closely follows the spiral arms, while in the outer Galaxy, the field is consistent being purely azimuthal. Furthermore, the models contain no reversals in the outer Galaxy, and together to suggest the existence of a single reversed region that spirals out from the Galactic center