High Galactic latitude polarized emission at 1.4 GHz and implications for cosmic microwave background observations

• Published in: Monthly notices of the Royal Astronomical Society 2005-03, Vol.358 (1), p.1-12
• Main Authors: Carretti, E., Bernardi, G., Sault, R. J., Cortiglioni, S., Poppi, S.
• Format: Article
• Language: English
• Subjects: cosmic microwave background; diffuse radiation; polarization; radiation mechanisms: non-thermal; radio continuum: ISM
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2005.08761.x

We analyse the polarized emission at 1.4 GHz in a 3°× 3° area at high Galactic latitude (b∼−40°). The region, centred in (α= 5h, δ=−49°), was observed with the Australia Telescope Compact Array (ATCA) radio-interferometer, whose 3–30 arcmin angular sensitivity range allows the study of scales appropriate for cosmic microwave background polarization (CMBP) investigations. The angular behaviour of the diffuse emission is analysed through the E- and B-mode angular power spectra. These follow a power law CXℓ∝ℓβX with slopes βE=−1.97 ± 0.08 and βB=−1.98 ± 0.07. The emission is found to be approximately a factor 25 fainter than in Galactic plane regions. The comparison of the power spectra with other surveys indicates that this area is intermediate between strong and negligible Faraday rotation effects. A similar conclusion can be reached by analysing both the frequency and Galactic latitude behaviours of the diffuse Galactic emission of the 408–1411 MHz Leiden survey data. We present an analysis of the Faraday rotation effects on the polarized power spectra and find that the observed power spectra can be enhanced by a transfer of power from large to small angular scales. The extrapolation of the spectra to 32 and 90 GHz of the cosmic microwave background (CMB) window suggests that Galactic synchrotron emission leaves the CMBP E-mode uncontaminated at 32 GHz. The level of the contamination at 90 GHz is expected to be more than 4 orders of magnitude below the CMBP spectrum. Extrapolating to the relevant angular scales, this region also appears adequate for investigation of the CMBP B-modes for models with tensor-to-scalar fluctuation power ratio T/S > 0.01. We also identify polarized point sources in the field, providing a nine object list, which is complete down to the polarized flux limit of Splim= 2 mJy.