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31st of July 2019
ATNF Colloquium
Multi-frequency polarimetry of a complete sample of faint PACO sources
Vincenzo Galluzzi (INAF - Istituto di Radioastronomia)
Abstract: The high-frequency (> 20 GHz), bright flux density (> 200 mJy) radio population is dominated by blazars. Their polarization properties are invaluable to study magnetic fields and plasma in the inner and unresolved regions of relativistic jets. For Cosmology, these objects constitute an important contaminant of CMB at scales smaller than 30’ up to 100 GHz, hence they hamper the detection of primordial B-modes associated to inflation. However, their properties are still poorly constrained: results in literature are easily affected by spectral, detection and variability-related biases.

We present an unbiased analysis of high sensitivity (σ_P ~ 0.6 mJy, ~90% detection rate at 5σ) multi-frequency (and multi-epoch) polarimetric observations for a complete sample of 104 compact extragalactic radio sources drawn from the faint (> 200 mJy at 20 GHz in total intensity) Planck-ATCA Coeval Observations (PACO) catalogue, performed with ATCA at 7 frequencies, over the 1.1-39 GHz frequency range. An ALMA project extends the analysis up to 100 GHz for a (complete) sub-sample of 32 objects. We classified our sources in terms of stuctural complexity, finding different behaviours in polarization fractions and position angles (PPA). We produce polarization differential source counts and assess forecasts for CMB studies.

The image above shows spectra in total intensity and polarization, polarization fractions and polarization angles for a selection of objects drawn from the faint PACO sample (Massardi et al. 2016), observed in the September 2014 and March-April 2016 campaigns (Galluzzi et al. 2018). The error bars are not displayed since they are smaller than the symbols. Total intensity flux densities: red pluses indicate our observations and the solid magenta lines show the fitting curves; the orange crosses show the median PACO flux densities (July 2009-August 2010); the brown triangles represent the AT20G observations (best epoch in 2004-2008). Linearly polarized flux densities: black pluses refer to our observations (upper limits are shown as black filled downwards triangles) and the solid blue lines indicate the best fit curves; AT20G observations (best epoch in 2004-2008) are represented by green diamonds. Other quantities (referring to September 2014 and March-April 2016 campaigns) are: linear polarization fractions, displayed as purple asterisks (upper limits are shown as downwards pointing purple filled triangles); circular polarization fraction, displayed as blue circles (downward triangles for upper limits); finally, polarization angles (PAs) are reported as black diamonds.

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