Lensing reconstruction from a patchwork of polarization maps

TL;DR

This paper investigates the feasibility of reconstructing gravitational lensing signals from a patchwork of small polarization maps obtained by ground-based telescopes, addressing noise biases and potential cosmological applications.

Contribution

It demonstrates that lensing reconstruction is feasible from patchwork maps despite noise biases, enabling cross-correlation and delensing applications.

Findings

Bias in B-mode power spectrum can be mitigated by removing large-scale B-modes.

Lensing potential can be reconstructed with negligible bias under certain noise conditions.

Reconstructed lensing signals can be used for cross-correlation with satellite data and delensing B-modes.

Abstract

The lensing signals involved in CMB polarization maps have already been measured with ground-based experiments such as SPTpol and POLARBEAR, and would become important as a probe of cosmological and astrophysical issues in the near future. Sizes of polarization maps from ground-based experiments are, however, limited by contamination of long wavelength modes of observational noise. To further extract the lensing signals, we explore feasibility of measuring lensing signals from a collection of small sky maps each of which is observed separately by a ground-based large telescope, i.e., lensing reconstruction from a patchwork map of large sky coverage organized from small sky patches. We show that, although the B-mode power spectrum obtained from the patchwork map is biased due to baseline uncertainty, bias on the lensing potential would be negligible if the B-mode on scales larger than the blowup scale of $1/f$ noise is removed in the lensing reconstruction. As examples of cosmological applications, we also show 1) the cross-correlations between the reconstructed lensing potential and full-sky temperature/polarization maps from satellite missions such as PLANCK and LiteBIRD, and 2) the use of the reconstructed potential for delensing B-mode polarization of LiteBIRD observation.