A fully sampled ë21 cm linear polarization survey of the southern sky

Abstract

Context: Linear polarization of Galactic synchrotron emission provides valuable information on the Galactic magnetic field and on the properties of the Galactic magneto-ionic medium. Polarized high-latitude Galactic emission is the major foreground for polarization studies of the cosmic microwave background. Aims: We present a new southern-sky ë21 cm linear polarization survey, which complements the recent ë21 cm DRAO northern sky polarization data. Methods: We used a 30-m telescope located at Villa Elisa/Argentina to map the southern sky simultaneously in continuum and linear polarization. Results: We present a fully sampled map of linearly polarized emission at ë21 cm of the southern sky for declinations between -10° and -90°. The angular resolution of the survey is 36' and its sensitivity is 15 mK (rms-noise) in Stokes U and Q. The survey's zero-level has been adjusted to that of the recent DRAO 1.4 GHz linear polarization survey by comparing data in the region of overlap between -10° and -27°. Conclusions: The polarized southern sky at 1.4 GHz shows large areas with smooth low-level emission almost uncorrelated to total intensities indicating that Faraday rotation originating in the Galactic interstellar medium along the line of sight is significant at 1.4 GHz. The southern sky is much less contaminated by local foreground features than is the northern sky. Thus high-frequency observations of polarized cosmic microwave emission are expected to be less affected. The percentage polarization of the high-latitude emission is low, which seems to be an intrinsic property of Galactic emission.