Multifrequency polarimetry of a complete sample of PACO radio sources

Abstract

We present high sensitivity polarimetric observations (σ P 0.6 mJy) in 6 bands covering the 5.5 − 38 GHz range of a complete sample of 53 compact extragalactic radio sources brighter than 200 mJy at 20 GHz. The observations, carried out with the Australia Telescope Compact Array (ATCA), achieved a 91% detection rate (at 5σ). Within this frequency range the spectra of about 95% of sources are well fitted by double power laws, both in total intensity and in polarisation, but the spectral shapes are generally different in the two cases. Most sources were classified as either steepor peaked-spectrum but less than 50% have the same classification in total and in polarised intensity. No significant trends of the polarisation degree with flux density or with frequency were found. The mean variability index in total intensity of steepspectrum sources increases with frequency for a 4 − 5 year lag, while no significant trend shows up for the other sources and for the 8 year lag. In polarisation, the variability index, that could be computed only for the 8 year lag, is substantially higher than in total intensity and has no significant frequency dependence.

Statistics of the fractional polarization of compact radio sources in Planck maps

“…At the lowest Planck frequencies and at high Galactic latitudes our present results are in general agreement with other published works on extragalactic radio sources (Sajina et al 2011;Massardi et al 2013;Galluzzi et al 2017). At higher frequencies we are presenting novel results that could be useful in estimating the polarized source number counts and, consequently, the contamination due to these sources for the detection of the primordial CMB E and B mode polarisation.…”

“…Sajina et al (2011) observed with the Very Large Array, for frequencies from 4.86 to 43.34 GHz, typical values for Π of 2 -5 per cent in a sample of sources selected in the AT20G catalogue with S20GHz > 40 mJy. More recently, Galluzzi et al (2017) found a median value for the polarisation fraction of 2.01 per cent at 33 GHz for their sample of 53 sources selected from the faint PACO sample (Bonavera et al 2011), with S20GHz > 200 mJy. They also found no trend with frequency or flux densities (up to 38 GHz) for Π, in agreement with our current findings.…”

“…For this reason, in our stacking procedure we decided to calculate Π = P0 / S and Π 2 = P 2 0 / S 2 that are good approximations for Π = P0/S and Π 2 = P 2 0 /S 2 , taking into account that Π and S can be considered independent variables (see e.g. Massardi et al (2008Massardi et al ( , 2013 and Galluzzi et al (2017) as discussed in Section 3.1). Besides, the residual errors introduced by these assumptions are much lower than the noise bias discussed in Section 2.3.…”

Statistics of the fractional polarization of extragalactic dusty sources in Planck HFI maps

“…The analysed sample of extragalactic dusty sources (selected from the 857 GHz of the PCCS2 catalogue) shows polarisation properties similar to those characterizing radio sources (Massardi et al 2013;Galluzzi et al 2017;B17). We measure polarization values of Π =(3.10 ± 0.75) per cent and Π = (3.65 ± 0.66) per cent at 217 and 353 GHz respectively, and of Π 2 =(7.38±1.32) per cent and (6.87±1.35) per cent at 217 and 353 GHz, respectively.…”

Fractional polarization of extragalactic sources in the 500 deg2 SPTpol survey

“…The results shown in Table 1 are consistent with previous studies of AGN and DSFGs. Briefly, in previous studies, polarisation fraction is found to be independent of flux (Battye et al 2011;Trombetti et al 2018;Datta et al 2018) and frequency (Battye et al 2011;Galluzzi et al 2017 Weighted Mean 6 − 1500 686 6.9 ± 1.1 2.63 ± 0.22 Table 1. Mean-squared polarisation fractions ( p 2 ) and inferred fractional polarisation ( p 2 ) measurements for Nsource number of SPT-SZ selected sources stacked in flux bins Srange using 95 and 150 GHz SPTpol maps.…”