Spin-SILC: CMB polarisation component separation with spin wavelets

TL;DR

Spin-SILC is a novel method using spin wavelets for accurate separation of CMB polarisation $E$ and $B$ modes from multifrequency microwave sky data, enabling concurrent component separation and $E$-$B$ decomposition.

Contribution

It introduces spin wavelets into the internal linear combination method, allowing simultaneous component separation and $E$-$B$ decomposition in CMB polarisation analysis.

Findings

Successfully recovers cosmological $E$ and $B$ modes from Planck simulations and data.

Demonstrates consistency with existing component separation methods.

Provides a computationally-efficient approach for future polarisation experiments.

Abstract

We present Spin-SILC, a new foreground component separation method that accurately extracts the cosmic microwave background (CMB) polarisation $E$ and $B$ modes from raw multifrequency Stokes $Q$ and $U$ measurements of the microwave sky. Spin-SILC is an internal linear combination method that uses spin wavelets to analyse the spin-2 polarisation signal $P = Q + iU$. The wavelets are additionally directional (non-axisymmetric). This allows different morphologies of signals to be separated and therefore the cleaning algorithm is localised using an additional domain of information. The advantage of spin wavelets over standard scalar wavelets is to simultaneously and self-consistently probe scales and directions in the polarisation signal $P = Q + iU$ and in the underlying $E$ and $B$ modes, therefore providing the ability to perform component separation and $E$-$B$ decomposition concurrently for the first time. We test Spin-SILC on full-mission Planck simulations and data and show the capacity to correctly recover the underlying cosmological $E$ and $B$ modes. We also demonstrate a strong consistency of our CMB maps with those derived from existing component separation methods. Spin-SILC can be combined with the pseudo- and pure $E$-$B$ spin wavelet estimators presented in a companion paper to reliably extract the cosmological signal in the presence of complicated sky cuts and noise. Therefore, it will provide a computationally-efficient method to accurately extract the CMB $E$ and $B$ modes for future polarisation experiments.