B–Mode contamination by synchrotron emission from 3-years WMAP 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-years 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 ∼ 16% and ∼ 26% 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 = 10–10 at 70-GHz in the 16% lowest emission sky (S/N < 2 area). These values worsen by a factor ∼ 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 ∼ 10 to be measured directly which approximately corresponds to the limit imposed by using a sky coverage of 15%. This opens interesting perspectives to investigate the inflationary model space in lowest emission regions.