Forecasting the Contribution of Polarized Extragalactic Radio Sources in CMB Observations

Abstract

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, (ν ≥ 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 ∼ 200 ( up to ∼ 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 < 0.05 and they have to be robustly controlled to de-lens CMB B-modes at the arcminute angular scales.

ALMA Band 3 polarimetric follow-up of a complete sample of faint PACO sources

“…The distribution of polarization fractions observed with ALMA allowed us to extend the analysis of Galluzzi et al (2018) up to 97.5 GHz, confirming the absence of any statistically significant trend with the frequency (or the flux density). This data set has been included in the analysis described in Puglisi et al (2018), which presents the stateof-the-art about polarimetry of extragalactic radio sources and provides forecasts for their contamination of the B-mode angular power spectrum, useful for current and forthcoming CMB experiments. Besides, our observed polarization fractions further confirm the results obtained from Planck maps by Bonavera et al (2017, adopting a stacking technique) and by Trombetti et al (2018, exploiting the intensity distribution analysis, IDA, method).…”

“…Distribution of the percentage polarization fraction at 97.5 GHz obtained with a bootstrap and re-sampling of the observed distribution of the polarization fractions (green points). The lognormal fit is shown by the blue solid line (the shaded area represents the 1σ uncertainty in the fitting curve, already presented byPuglisi et al 2018). We also plot the distribution obtained byBonavera et al (2017, the orange dashed line with the corresponding 1σ shaded area).…”

The Simons Observatory: science goals and forecasts

“…8. A more realistic estimate of the polarized source level comes from Puglisi et al (2017), who combine state-ofthe-art catalogs of polarized radio sources at frequencies ranging from 1.4 to 217 GHz, to derive the statistical properties of fractional polarization, Π = P/S. They find Π 2 to have a roughly constant value, 2.5 × 10 −3 .…”

Evidence for the Cross-correlation between Cosmic Microwave Background Polarization Lensing from Polarbear and Cosmic Shear from Subaru Hyper Suprime-Cam

“…the 25 mJy detection threshold contribute a residual power, but Smith et al (2009) and Puglisi et al (2018) show that this level of contribution is negligible in lensing auto-spectra.…”