Predictions on the high-frequency polarization properties of extragalactic radio sources and implications for polarization measurements of the cosmic microwave background

Abstract

We present a method to simulate the polarization properties of extragalactic radio sources at microwave frequencies. Polarization measurements of nearly 2 x 10 6 sources at 1.4 GHz are provided by the NVSS survey. Using this catalogue and the GB6 survey, we study the distribution of the polarization degree of both steep- and flat-spectrum sources. We find that the polarization degree is anticorrelated with the flux density for the former population, while no correlation is detected for the latter. The available high-frequency data are exploited to determine the frequency dependence of the distribution of polarization degrees. Using such information and the evolutionary model developed by Toffolatti and coworkers, we estimate the polarization power spectra of extragalactic radio sources at ≥30 GHz and their contamination of CMB polarization maps. Two distinct methods to compute point-source polarization spectra are presented, extending and improving the one generally used in previous analyses. While extragalactic radio sources can significantly contaminate the CMB E-mode power spectrum only at low frequencies (ν? 30 GHz), they can severely constrain the detectability of the CMB B mode up to ν ≃ 100 GHz.