Radio polarization from the inner galaxy at arcminute resolution

The Southern Galactic Plane Survey (SGPS) is an H I and 1.4 GHz continuum s urvey of the fourth quadrant of the Galaxy at arcminute resolution. We pres ent here results on linearly polarized continuum emission from an initial 2 8 deg(2) test region for the SGPS, consisting of 190 mosaicked pointings of the Australia Telescope Compact Array and covering the range 325.degrees5 < l < 332.degrees5, -0.degrees5 < b < 3.degrees5. Complicated extended stru cture is seen in linear polarization throughout the test region, almost all of which has no correlation with total intensity. We interpret the brighte st regions of polarized emission as representing intrinsic structure in ext ended polarization, most likely originating in the Crux spiral arm at a dis tance of 3.5 kpc; fainter polarized structure is imposed by Faraday rotatio n in foreground material. Two large areas in the field are devoid of polari zation. We argue that these voids are produced by foreground H II regions i n which the magnetic field is disordered on scales of similar to0.1-0.2 pc. We also identify a depolarized halo around the H II region RCW 94, which w e suggest results from the interaction of the H II region with a surroundin g molecular cloud.