Forecasting Polarized Radio Sources for CMB observations
  We combine the latest datasets obtained with different surveys to study the
frequency dependence of polarized emission coming from Extragalactic Radio
Sources (ERS). We consider data over a very wide frequency range starting from
$1.4$ GHz up to $217$ GHz. This range is particularly interesting since it
overlaps the frequencies of the current and forthcoming Cosmic Microwave
Background (\cmb) experiments. Current data suggest that at high radio
frequencies, ($ \nu \geq 20$ GHz) the fractional polarization of ERS does not
depend on the total flux density. Conversely, recent datasets indicate a
moderate increase of polarization fraction as a function of frequency,
physically motivated by the fact that Faraday depolarization is expected to be
less relevant at high radio-frequencies. We compute ERS number counts using
updated models based on recent data, and we forecast the contribution of
unresolved ERS in CMB polarization spectra. Given the expected sensitivities
and the observational patch sizes of forthcoming \cmb\ experiments about $\sim
200 $ ( up to $\sim 2000 $ ) polarized ERS are expected to be detected.
Finally, we assess that polarized ERS can contaminate the cosmological B-mode
polarization if the tensor-to-scalar ratio is $r< 0.05$ and they have to be
robustly controlled to de-lens \cmb\ B-modes at the arcminute angular scales.
