Multitracer CMB delensing maps from Planck and WISE data

Abstract

Delensing, the removal of the limiting lensing $B$-mode background, is crucial for the success of future cosmic microwave background (CMB) surveys in constraining inflationary gravitational waves (IGWs). In recent work, delensing with large-scale structure tracers has emerged as a promising method both for improving constraints on IGWs and for testing delensing methods for future use. However, the delensing fractions (i.e., the fraction of the lensing-$B$ mode power removed) achieved by recent efforts have been only 20%--30%. In this work, we provide a detailed characterization of a full-sky, dust-cleaned cosmic infrared background (CIB) map for delensing and construct a further-improved delensing template by adding additional tracers to increase delensing performance. In particular, we build a multitracer delensing template by combining the dust-cleaned Planck CIB map with a reconstructed CMB lensing map from Planck and a galaxy number density map from the Wide-field Infrared Survey Explorer (WISE) satellite. For this combination, we calculate the relevant weightings by fitting smooth templates to measurements of all the cross-spectra and autospectra of these maps. On a large fraction of the sky (${f}_{\mathrm{sky}}=0.43$), we demonstrate that our maps are capable of providing a delensing factor of $43\ifmmode\pm\else\textpm\fi{}1%$; using a more restrictive mask (${f}_{\mathrm{sky}}=0.11$), the delensing factor reaches $48\ifmmode\pm\else\textpm\fi{}1%$. For low-noise surveys, our delensing maps, which cover much of the sky, can thus improve constraints on the tensor-to-scalar ratio ($r$) by nearly a factor of 2. The delensing tracer maps are made publicly available, and we encourage their use in ongoing and upcoming $B$-mode surveys.