Absolutely calibrated radio polarimetry of the inner Galaxy at 2.3 GHz
  and 4.8 GHz
  We present high sensitivity and absolutely calibrated images of diffuse radio
polarisation at a resolution of about 10 arcmin covering the range 10 degr
<l<34 degr and |b|<5 degr at 2.3 GHz from the S-band Parkes All Sky Survey and
at 4.8 GHz from the Sino-German 6 cm polarisation survey of the Galactic plane.
Strong depolarisation near the Galactic plane is seen at 2.3 GHz, which
correlates with strong Halpha emission. We ascribe the depolarisation to
spatial Faraday rotation measure fluctuations of about 65 rad/m2 on scales
smaller than 6-9 pc. We argue that most (about 90%) of the polarised emission
seen at 4.8 GHz originates from a distance of 3-4 kpc in the Scutum arm and
that the random magnetic field dominates the regular field there. A branch
extending from the North Polar Spur towards lower latitudes can be identified
from the polarisation image at 4.8 GHz but only partly from the polarised image
at 2.3 GHz, implying the branch is at a distance larger than 2-3 kpc. We show
that comparison of structure functions of complex polarised intensity with
those of polarised intensity can indicate whether the observed polarised
structures are intrinsic or caused by Faraday screens. The probability
distribution function of gradients from the polarisation images at 2.3 GHz
indicates the turbulence in the warm ionised medium is transonic.
