Large Scale Polarization from Planck
Résumé
This paper describes the likelihood analysis of large scale polarization signalperformed by the Planck collaboration for the 2015 relase based on the PlanckLow Frequency Instrument (LFI) and for the 2016 intermediate analysis based onHigh Frequency Instrument (HFI). The 70 GHz LFI map, cleaned from synchrotronand dust emission, allows to detect Thomson scattering optical depth τ over 2 −σ level, namely τ = 0.067 ± 0.023. The cross-spectrum between 100 and 143 GHzmaps measured by HFI, cleaned from foreground contaminations and from residualsystematics as well, provides a more stringent constrain, i.e. τ = 0.055 ±0.009. Those results are substantially lower than previous measurements made byWMAP team and now fully consistent with astrophysical observations of highredshift sources.