The S-PASS view of polarized Galactic Synchrotron at 2.3 GHz as a
  contaminant to CMB observations
  We analyze the Southern Sky emission in linear polarization at 2.3 GHz as
observed by the S-band Polarization All Sky Survey S-PASS. Our purpose is to
study the properties of the diffuse Galactic polarized synchrotron as a
contaminant to CMB B-mode observations. We study the angular distribution of
the S-PASS signal at intermediate and high Galactic latitudes by means of
angular power spectra. Power spectra, show a decay of the spectral amplitude as
a function of multipole for \ell<200, typical of the diffuse emission. Spectra
can be approximated by a power law C_{\ell}\propto\ell^{alpha}, with alpha~-3,
and characterized by a B-to-E ratio of ~0.5. We study the synchrotron SED in
polarization by computing power spectra of the low frequency WMAP and Planck
maps. Results show that the SED, in the frequency range 2.3-33 GHz, is
compatible with a power law with beta_s=-3.22\pm0.08. Combining S-PASS
polarization maps with those coming from WMAP and Planck we derived a map of
the synchrotron spectral index at angular resolution of 2{\deg} on about 30% of
the sky. The recovered distribution peaks at the value around -3.2. We also
measure a significant spatial correlation between synchrotron and thermal dust
signals, as traced by the Planck 353 GHz channel. This correlation reaches
about 40% on the larger angular scales, decaying considerably at the degree
scales. Finally, we use the S-PASS maps to assess the polarized synchrotron
contamination to CMB observations of the B-modes. Moreover, by combining S-PASS
data with Planck 353 GHz observations, we recover a map of the minimum level of
total polarized foreground contamination to B-modes, finding that there is no
region of the sky, at any frequency, where this contamination lies below
equivalent tenor-to-scalar ratio ~10^-3. This result confirms the importance of
observing both high and low frequency foregrounds in CMB B-mode measurements.
