2014MNRAS.437.2936S

We present high-sensitivity and absolutely calibrated images of diffuse radio polarization at a resolution of about 10arcmin covering the range 10° < l < 34° and {verbar}b{verbar} < 5° at 2.3GHz from the S-band Polarization All Sky Survey and at 4.8GHz from the Sino-German λ6cm polarization survey of the Galactic plane. Strong depolarization near the Galactic plane is seen at 2.3GHz, which correlates with strong Hα emission. We ascribe the depolarization to spatial Faraday rotation measure fluctuations of about 65 rad/m2 on scales smaller than 6-9pc. We argue that most (about 90 percent) of the polarized emission seen at 4.8GHz originates from a distance of 3-4kpc 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 polarization image at 4.8GHz but only partly from the polarization image at 2.3GHz, implying that the branch is at a distance larger than 2-3kpc. We show that comparison of structure functions of complex polarized intensity with those of polarized intensity can indicate whether the observed polarized structures are intrinsic or caused by Faraday screens. The probability distribution function of gradients from the polarization images at 2.3GHz indicates that the turbulence in the warm ionized medium is transonic.