B-mode contamination by synchrotron emission from 3-yr Wilkinson Microwave Anisotropy Probe data

We study the contamination of the B-mode of the cosmic microwave background polarization (CMBP) by Galactic synchrotron in the lowest emission regions of the sky. The 22.8-GHz polarization map of the 3-yr Wilkinson Microwave Anisotropy Probe (WMAP) data release is used to identify and analyse such regions. Two areas are selected with signal-to-noise ratio S/N < 2 and S/N < 3, covering similar to 16 and similar to 26 per cent fraction of the sky, respectively. The polarization power spectra of these two areas are dominated by the sky signal on large angular scales (multipoles l < 15), while the noise prevails on degree scales. Angular extrapolations show that the synchrotron emission competes with the CMBP B-mode signal for tensor-to-scalar perturbation power ratio T/S = 10(-3)-10(-2) at 70 GHz in the 16 per cent lowest emission sky (S/N < 2 area). These values worsen by a factor similar to 5 in the S/N < 3 region. The novelty is that our estimates regard the whole lowest emission regions and outline a contamination better than that of the whole high Galactic latitude sky found by the WMAP team (T/S > 0.3). Such regions allow T/S similar to 10(-3) to be measured directly which approximately corresponds to the limit imposed by using a sky coverage of 15 per cent. This opens interesting perspectives on the investigation of the inflationary model space in lowest emission regions.