Foreground removal requirements for measuring large-scale CMB B-modes in light of BICEP2

TL;DR

This paper evaluates the foreground removal accuracy needed for large-scale CMB B-mode measurements to confirm BICEP2's findings, showing that current and future experiments can improve constraints on the tensor-to-scalar ratio r.

Contribution

It provides forecasts for the required foreground cleaning precision for large-scale B-mode detection using simulated experiments, highlighting the importance for current and future missions.

Findings

Planck can confirm r=0.1-0.2 without instrumental systematics

Combining Planck with BICEP2 improves r constraints by 25-45%

Next-generation satellites like COrE can significantly reduce uncertainty on r

Abstract

The most convincing confirmation that the B-mode polarization signal detected at degree scales by BICEP2 is due to the Cosmic Microwave Background (CMB) would be the measurement of its large-scale counterpart. We assess the requirements for diffuse component separation accuracy over large portions of the sky in order to measure the large-scale B-mode signal corresponding to a tensor to scalar ratio of r=0.1-0.2. We use the method proposed by Bonaldi & Ricciardi (2011) to forecast the performances of different simulated experiments taking into account noise and foreground removal issues. We do not consider instrumental systematics, and we implicitly assume that they are not the dominant source of error. If this is the case, the confirmation of an r=0.1-0.2 signal is achievable by Planck even for conservative assumptions regarding the accuracy of foreground cleaning. Our forecasts suggest that the combination of this experiment with BICEP2 will lead to an improvement of 25-45% in the constraint on r. A next-generation CMB polarization satellite, represented in this work by the COrE experiment, can reduce dramatically (by almost another order of magnitude) the uncertainty on r. In this case, however, the accuracy of foreground removal becomes critical to fully benefit from the increase in sensitivity.