Sensitivity and foreground modelling for large-scale CMB B-mode polarization satellite missions

TL;DR

This paper evaluates how foreground modelling inaccuracies affect the detection of primordial B-mode polarization in future CMB satellite missions, emphasizing the importance of precise component separation for accurate tensor-to-scalar ratio estimation.

Contribution

It compares the sensitivity of various CMB satellite concepts to foreground modelling errors and quantifies their impact on primordial B-mode detection.

Findings

Incorrect dust component modelling biases tensor-to-scalar ratio by over 5σ.

Neglecting synchrotron spectral curvature biases ratio by over 1σ.

Omitting spinning dust can cause significant bias in sensitive experiments.

Abstract

The measurement of the large-scale B-mode polarization in the cosmic microwave background (CMB) is a fundamental goal of future CMB experiments. However, because of unprecedented sensitivity, future CMB experiments will be much more sensitive to any imperfect modelling of the Galactic foreground polarization in the reconstruction of the primordial B-mode signal. We compare the sensitivity to B-modes of different concepts of CMB satellite missions (LiteBIRD, COrE, COrE+, PRISM, EPIC, PIXIE) in the presence of Galactic foregrounds. In particular, we quantify the impact on the tensor-to-scalar parameter of incorrect foreground modelling in the component separation process. Using Bayesian fitting and Gibbs sampling, we perform the separation of the CMB and Galactic foreground B-modes. The recovered CMB B-mode power spectrum is used to compute the likelihood distribution of the tensor-to-scalar ratio. We focus the analysis to the very large angular scales that can be probed only by CMB space missions, i.e. the Reionization bump, where primordial B-modes dominate over spurious B-modes induced by gravitational lensing. We find that fitting a single modified blackbody component for thermal dust where the "real" sky consists of two dust components strongly bias the estimation of the tensor-to-scalar ratio by more than 5{\sigma} for the most sensitive experiments. Neglecting in the parametric model the curvature of the synchrotron spectral index may bias the estimated tensor-to-scalar ratio by more than 1{\sigma}. For sensitive CMB experiments, omitting in the foreground modelling a 1% polarized spinning dust component may induce a non-negligible bias in the estimated tensor-to-scalar ratio.