Characterization of foreground emission at degree angular scale for CMB
  B-modes observations. Thermal Dust and Synchrotron signal from Planck and
  WMAP data
  We quantify the contamination from polarized diffuse Galactic synchrotron and
thermal dust emissions to the B-modes of the CMB anisotropies on the degree
angular scale, using data from the Planck and WMAP satellites. We compute power
spectra of foreground polarized emissions in 352 circular sky patches located
at Galactic latitude |b|>20{\deg}, each of which covering a fraction of the sky
of about 1.5%. We make use of the spectral properties derived from Planck and
WMAP data to extrapolate, in frequency, the amplitude of synchrotron and
thermal dust B-modes spectra in the multipole bin centered at $\ell\simeq80$.
In this way we estimate, for each analyzed region, the amplitude and frequency
of the foreground minimum. We detect both dust and synchrotron signal, at
degree angular scale and at 3 confidence level, in 28 regions. Here the minimum
of the foreground emission is found at frequencies between 60 and 100 GHz with
an amplitude,expressed in terms of the equivalent tensor-to-scalar ratio, r_FG,
between ~0.06 and ~1. Some of these regions are located at high Galactic
latitudes, in areas close to the ones which are being observed by sub-orbital
experiments.In all the other sky patches, where synchrotron or dust B-modes are
not detectable with the required confidence, we put upper limits on the minimum
foreground contamination and find values of r_FG between ~0.05 and ~1.5, in the
frequency range 60-90 GHz. Our results indicate that, with the current
sensitivity at low frequency, it is not possible to exclude the presence of
synchrotron contamination to CMB cosmological B-modes at the level requested to
measure a gravitational waves signal with r~0.01, at frequency <100 GHz,
anywhere. Therefore, more accurate data are essential in order to better
characterize the synchrotron polarized component, and eventually, remove its
contamination to CMB signal through foreground cleaning.
