ForegroundImmune Cosmic Microwave Background Lensing with ShearOnly Reconstruction
Abstract
Cosmic microwave background (CMB) lensing from current and upcoming widefield CMB experiments such as AdvACT, SPT3G and Simons Observatory relies heavily on temperature (versus polarization). In this regime, foreground contamination to the temperature map produces significant lensing biases, which cannot be fully controlled by multifrequency component separation, masking, or bias hardening. In this Letter, we split the standard CMB lensing quadratic estimator into a new set of optimal "multipole" estimators. On large scales, these multipole estimators reduce to the known magnification and shear estimators, and a new shear B mode estimator. We leverage the different symmetries of the lensed CMB and extragalactic foregrounds to argue that the shearonly estimator should be approximately immune to extragalactic foregrounds. We build a new method to compute, separately and without noise, the primary, secondary, and trispectrum biases to CMB lensing from foreground simulations. Using this method, we demonstrate that the shear estimator is, indeed, insensitive to extragalactic foregrounds, even when applied to a singlefrequency temperature map contaminated with cosmic infrared background, thermal SunyaevZel'dovich, kinematic SunyaevZel'dovich, and radio point sources. This dramatic reduction in foreground biases allows us to include higher temperature multipoles than with the standard quadratic estimator, thus, increasing the total lensing signaltonoise ratio beyond the quadratic estimator. In addition, magnificationonly and shear B mode estimators provide useful diagnostics for potential residuals.
 Publication:

Physical Review Letters
 Pub Date:
 May 2019
 DOI:
 10.1103/PhysRevLett.122.181301
 arXiv:
 arXiv:1804.06403
 Bibcode:
 2019PhRvL.122r1301S
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 New "multipole" estimators, code available at https://github.com/EmmanuelSchaan/LensQuEst