Impact of Galactic polarized emission on B-mode detection at low multipoles

TL;DR

This paper evaluates how polarized Galactic emission affects the detection of primordial B-modes at low multipoles, demonstrating the limitations and proposing a template fitting method for foreground removal using Planck data.

Contribution

It introduces a simple, robust template fitting technique for foreground subtraction in noisy polarization data and assesses the fundamental detection limit of r around 0.1 due to Galactic foregrounds.

Findings

Offset caused by E-mode polarization sets a detection limit of r ≈ 0.1.

Template fitting can recover primordial B-modes despite foreground contamination.

Foreground subtraction methods are feasible with Planck data even with noise.

Abstract

We use a model of polarized Galactic emission developed by the the Planck collaboration to assess the impact of foregrounds on B-mode detection at low multipoles. Our main interest is to applications of noisy polarization data and in particular to 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 analyze internal linear combination techniques and show that the offset caused by the dominant E-mode polarization pattern leads to a fundamental limit of r approximately 0.1 for the tensor-scalar ratio even in the absence of instrumental noise. We devise a simple, robust, template fitting technique using multi-frequency 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.