Impact of Galactic polarized emission onB-mode detection at low multipoles

We use a model of polarized Galactic emission developed by the Planck collaboration to assess the impact of foregrounds on B-mode detection at low multipoles. Our main interest is in applications of noisy polarization data and in particular in assessing the feasibility of B-mode detection by Planck. This limits the complexity of foreground subtraction techniques that can be applied to the data. We analyse internal linear combination techniques and show that the offset caused by the dominant E-mode polarization pattern leads to a fundamental limit of r∼ 0.1 for the tensor–scalar ratio even in the absence of instrumental noise. We devise a simple, robust, template fitting technique using multifrequency polarization maps. We show that template fitting using Planck data alone offers a feasible way of recovering primordial B-modes from dominant foreground contamination, even in the presence of noise on the data and templates. We implement and test a pixel-based scheme for computing the likelihood function of cosmological parameters at low multipoles that incorporates foreground subtraction of noisy data.