Simple foreground cleaning algorithm for detecting primordial B-mode polarization of the cosmic microwave background

TL;DR

This paper demonstrates a simple pixel-based foreground removal method for detecting primordial B-mode polarization in the CMB, achieving low residual bias in tensor-to-scalar ratio estimates with minimal frequency channels.

Contribution

It revisits and validates a foreground cleaning algorithm for future CMB experiments, showing its effectiveness with only three frequency channels and no external templates.

Findings

Residual bias in r as low as 0.002 with 3 frequencies

Bias reduced to below 0.001 with extended masking

Method effective for next-generation low-noise CMB experiments

Abstract

We reconsider the pixel-based, "template" polarized foreground removal method within the context of a next-generation, low-noise, low-resolution (0.5 degree FWHM) space-borne experiment measuring the cosmological B-mode polarization signal in the cosmic microwave background (CMB). This method was put forward by the Wilkinson Microwave Anisotropy Probe (WMAP) team and further studied by Efstathiou et al. We need at least 3 frequency channels: one is used for extracting the CMB signal, whereas the other two are used to estimate the spatial distribution of the polarized dust and synchrotron emission. No external template maps are used. We extract the tensor-to-scalar ratio (r) from simulated sky maps consisting of CMB, noise (2 micro K arcmin), and a foreground model, and find that, even for the simplest 3-frequency configuration with 60, 100, and 240 GHz, the residual bias in r is as small as Delta r~0.002. This bias is dominated by the residual synchrotron emission due to spatial variations of the synchrotron spectral index. With an extended mask with fsky=0.5, the bias is reduced further down to <0.001.