Impact of modelling foreground uncertainties on future CMB polarization satellite experiments

Abstract

We present an analysis of errors on the tensor-to-scalar ratio due to residual diffuse foregrounds. We use simulated observations of a CMB polarization satellite, the Cosmic Origins Explorer, using the specifications of the version proposed to ESA in 2010 (COrE). We construct a full pipeline from microwave sky maps to $r$ likelihood, using two models of diffuse Galactic foregrounds with different complexity, and assuming component separation with varying degrees of accuracy. Our pipeline uses a linear mixture (Generalized Least Squares) solution for component separation, and a hybrid approach for power spectrum estimation, with a Quadratic Maximum Likelihood estimator at low $\ell$s and a pseudo-$C_{\ell }$ deconvolution at high $\ell$s. In the likelihood for $r$, we explore modelling foreground residuals as nuisance parameters. Our analysis aims at measuring the bias introduced in $r$ by mismodelling the foregrounds, and to determine what error is tolerable while still successfully detecting $r$. We find that $r=0.01$ can be measured successfully even for a complex sky model and in the presence of foreground parameters error. However, the detection of $r=0.001$ is a lot more challenging, as inaccurate modelling of the foreground spectral properties may result in a biased measurement of $r$. Once biases are eliminated, the total error on $r$ allows setting an upper limit rather than a detection, unless the uncertainties on the foreground spectral indices are very small, i.e. equal or better than 0.5\% error for both dust and synchrotron. This emphasizes the need for pursuing research on component separation and foreground characterization in view of next-generation CMB polarization experiments.

13 pages, 11 figures and 4 tables. Accepted for publication by MNRAS

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• Characterizing bias on large scale CMB $B$-modes after galactic foregrounds cleaning
• The Simons Observatory: pipeline comparison and validation for large-scale B-modes
• Joint Bayesian estimation of tensor and lensing B-modes in the power spectrum of CMB polarization data
• Galactic foreground constraints on primordial $B$-mode detection for ground-based experiments
• A Bayesian ILC method for CMB B-mode posterior estimation and reconstruction of primordial gravity wave signal
• Do We Have Sufficient Knowledge of the Galactic Foreground Emission in Cosmic Microwave Background Science?