The Galactic Magneto-Ionic Medium Survey: Moments of the Faraday Spectra
  Faraday rotation occurs along every line of sight in the Galaxy; Rotation
Measure (RM) synthesis allows a three-dimensional representation of the
interstellar magnetic field. This study uses data from the Global Magneto-Ionic
Medium Survey, a combination of single-antenna spectro-polarimetric studies,
including northern sky data from the DRAO 26-m Telescope (1270-1750 MHz) and
southern sky data from the Parkes 64-m Telescope (300-480 MHz). From the
synthesized Faraday spectral cubes we compute the zeroth, first, and second
moments to find the total polarized emission, mean and RM-width of the
polarized emission. From DRAO first moments we find a weak vertical field
directed from Galactic North to South, but Parkes data reveal fields directed
towards the Sun at high latitudes in both hemispheres: the two surveys clearly
sample different volumes. DRAO second moments show feature widths in Faraday
spectra increasing with decreasing positive latitudes, implying that longer
lines of sight encounter more Faraday rotating medium, but this is not seen at
negative latitudes. Parkes data show the opposite: at positive latitudes the
second moment decreases with decreasing latitude, but not at negative
latitudes. Comparing first moments with RMs of pulsars and extragalactic
sources and a study of depolarization together confirm that the DRAO survey
samples to larger distances than the Parkes data. Emission regions in the DRAO
survey are typically 700 to 1000 pc away, slightly beyond the scale-height of
the magneto-ionic medium; emission detected in the Parkes survey is entirely
within the magneto-ionic disk, less than 500 pc away.
