Deriving the global structure of the galactic magnetic field from faraday rotation measures of extragalactic sources

Abstract

We made use of the two latest sets of rotation measures (RMs) of extragalactic radio sources, namely the NRAO VLA Sky Survey rotation measures catalog and a compilation by Kronberg and Newton-McGee, to infer the global structure of the Galactic magnetic field (GMF). We have checked that these two data sets are mutually consistent. Given the existence of clear patterns in the all-sky RM distributions we considered GMF models consisting of two components: disk (spiral or ring) and halo. The parameters of these components were determined by fitting different model field geometries to the observedRMs. We found that the model consisting of a symmetric (with respect to the Galactic plane) spiral disk and antisymmetric halo fits the data best and reproduces the observed distribution ofRMs over the sky very well. We confirm that ring disk models are disfavored. Our results favor small pitch angles around - 5° and an increased vertical scale of electron distribution, in agreement with some recent studies. Based on our fits, we select two benchmark models suitable for studies of cosmic ray propagation, including cosmic rays at ultrahigh energies. © 2011. The American Astronomical Society. All rights reserved.