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 \sim 16 % and \sim 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 \ell < 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 % lowest emission sky ( S / N < 2 area ) .
These values worsen by a factor \sim 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 \sim 10 ^ { -3 } 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 .