Polarized radio emission over the southern Galactic plane at 2.4 GHz

Abstract

Polarimetric results from the Parkes 2.4-GHz survey of the southern Galactic plane are presented. These take the form of a series of images, detailing the polarized intensity and vector position angles over the survey area. The observations were made using the 64-m Parkes radio telescope, and cover the Galactic plane within the region 238°≤l≤5°, with a latitude range of at least |b|≤5°, with some coverage to b = +7° and b = -8°. The resolution of the images is 10.4 arcmin. The rms noise of the polarized intensity images is 11 mJy beam area-1 (5.3 mK), and the rms variation in the vector position angles is of the order of several dgrees. The images show many polarized structures, over a wide range of intensities and angular sizes. Bright, extended regions of polarized emission (of the order of 5° across) are detected, including the Vela supernova remnant and a large 'cap' structure appearing to the north of Sgr A. A quasi-uniform 'background' component of faint, patchy emission is seen over the length of the survey. This faint component appears to originate over a range of distances, out to greater than 5 kpc, and shows considerable structure in the orientations of the polarization vectors. Several bright H II complexes are seen to exhibit bipolar, depolarizing 'plumes', several degrees in length, which are interpreted as outflows of low-density thermal material (with densities in the range 1-10 cm-3).