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

Abstract

We present Atacama Large Millimeter/submillimiter Array (ALMA) high sensitivity (${\sigma }_P\simeq 0.4$mJy) polarimetric observations at $97.5$GHz (Band 3) of a complete sample of $32$ extragalactic radio sources drawn from the faint Planck-ATCA Co-eval Observations (PACO) sample ($b<-75^{\circ }$, compact sources brighter than $200$mJy at $20$GHz). We achieved a detection rate of $97\%$ at $3\sigma$ (only $1$ non-detection). We complement these observations with new Australia Telescope Compact Array (ATCA) data between $2.1$ and $35$GHz obtained within a few months and with data published in earlier papers from our collaboration. Adding the co-eval GaLactic and Extragalactic All-sky Murchison widefield array (GLEAM) survey detections between $70$ and $230$MHz for our sources, we present spectra over more than $3$ decades in frequency in total intensity and over about $1.7$ decades in polarization. The spectra of our sources are smooth over the whole frequency range, with no sign of dust emission from the host galaxy at mm wavelengths nor of a sharp high frequency decline due, for example, to electron ageing. We do however find indications of multiple emitting components and present a classification based on the number of detected components. We analyze the polarization fraction behaviour and distributions up to $97$GHz for different source classes. Source counts in polarization are presented at $95$GHz.

18 pages, 11 figures, accepted for publication in MNRAS

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• A Bayesian method for point source polarization estimation
• Extragalactic astrophysics with next-generation CMB experiments