Multi-frequency polarimetry of a complete sample of PACO radio sources

The high-frequency (> 20 GHz) bright flux density (> 200 mJy) radio population is dominated by blazars but their polarization properties are still poorly constrained: the latter are informative about magnetic fields and plasma in inner regions of relativistic jets. Cosmologically, extragalactic radio sources are an important contaminant to the CMB at scales smaller than 30' up to 100 GHz, hence crucial in the search for primordial B-modes. We present the results of ALMA 100 GHz polarimetric observations of 32 radio sources, selected as a complete subsample of 104 sources already observed with high sensitivity (~ 0.6 mJy) in 7 frequency bands (1.1-39 GHz) with ATCA. We confirmed polarization spectra of single sources cannot be simply inferred from total intensity ones, as different source components dominate the different emissions; we find complex behaviours in polarization fractions and polarization position angles (PPAs). Moreover, the observations are useful to assess statistical and systematic accuracies of PPA obtained with ALMA and to explore its use for calibrating CMB experiments. Dedicated analysis of few peculiar objects in our sample will be also shown.