Map-based E/B separation of filtered timestreams using space-based E-mode observations

Abstract

E to B mixing or "leakage" due to time-ordered data (TOD) filtering has become an important source of sensitivity loss that ground-based cosmic microwave background polarization experiments must address. However, it is a difficult problem for which very few viable solutions exist. In this paper, we expand upon satellite E-mode methods to cover E/B leakage specifically due to TOD filtering. We take a satellite E-mode map and TOD filter it through the ground-based experiment data analysis pipeline, from which we construct a map-space "leakage template" and subtract it from the ground-based experiment map. We evaluate the residual leakage by simulating the satellite E-mode maps with Planck-like and LiteBIRD-like noise levels, and simulate the ground-based experiment with Simons Observatory-like and CMB-S4-like noise levels. The effectiveness of the method is measured in the improvement of the Fisher uncertainty $\sigma(r=0)$. We find that our method can reduce $\sigma(r=0)$ by $\sim15\text{--}75\%$ depending on the noise levels considered.