Determining the Magnetic Field in the Galactic Plane from New Arecibo Pulsar Faraday Rotation Measurements

TL;DR

This paper introduces a new method for mapping the Galactic magnetic field using pulsar Faraday rotation measures, revealing complex field structures and reversals along spiral arms.

Contribution

The authors develop a geometrically-corrected, arm-by-arm analysis technique for pulsar RMs, improving the understanding of magnetic field variations in the Galactic plane.

Findings

Disparities in magnetic field magnitude above and below the plane in multiple spiral arms.

Evidence for a latitude-dependent magnetic field reversal near the Local/Sagittarius boundary.

Identification of a single magnetic field reversal near the Local/Sagittarius arm boundary.

Abstract

We develop a new method for studying the Galactic magnetic field along the spiral arms using pulsar Faraday rotation measures (RMs). Our new technique accounts for the dot-product nature of Faraday rotation and also splits the associated path integral into segments corresponding to particular zones along the LOS. We apply this geometrically-corrected, arm-by-arm technique to the low-latitude portion of a recently published set of Arecibo Faraday RMs for 313 pulsars along with previously obtained RMs in the same regions. We find disparities $>1\sigma$ between the magnitude of the field above and below the plane in the Local Arm, Sagittarius Arm, Sagittarius-to-Scutum Interarm, the Scutum Arm, and Perseus Arm. We find evidence for a single field reversal near the Local/Sagittarius arm boundary. Interestingly, our results suggest that this field reversal is dependent on latitude, occurring inside the Sagittarius arm at negative Galactic latitudes and at the Local-to-Sagittarius Arm boundary at positive Galactic latitudes. We discuss all of our results in the context of different models and other observational Galactic magnetic field analyses.