Deriving global structure of the Galactic Magnetic Field from Faraday Rotation Measures of extragalactic sources

TL;DR

This study uses recent extragalactic radio source data to model the Galactic Magnetic Field, finding a best fit with a symmetric spiral disk and anti-symmetric halo, which aids cosmic ray research.

Contribution

First comprehensive modeling of the Galactic Magnetic Field using the latest RM data, identifying a preferred symmetric spiral disk and anti-symmetric halo configuration.

Findings

Best fit model includes symmetric spiral disk and anti-symmetric halo

Ring disk models are disfavored by the data

Results support small pitch angles (~ -5 degrees) and increased vertical electron scale height

Abstract

We made use of the two latest sets of Rotational Measures (RMs) of extra-galactic radio sources, namely the NRAO VLA Sky Survey otation Measures Catalogue, and a compilation by Kronberg&Newton-McGee(2011), to infer the global structure of the Galactic Magnetic Field (GMF). We have checked that these two data sets are consistent with each other. Motivated by clear patterns in the observed distribution of RMs over the sky, we considered GMF models consisting of the two components: disk (spiral or ring) and halo. The parameters of these components were determined by fitting different model field geometries to the observed RMs. We found that the model consisting of a symmetric (with respect to the Galactic plane) spiral disk and anti-symmetric halo fits the data best, and reproduces the observed distribution of RMs over the sky very well. We confirm that ring disk models are disfavored. Our results favor small pitch angles around -5 degrees and an increased vertical scale of electron distribution, in agreement with some previous studies. Based on our fits, we identify two benchmark models suitable for studies of cosmic ray propagation, including the ultra-high energies.