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