Foreground-Immune Cosmic Microwave Background Lensing with Shear-Only Reconstruction

Area of Science:

• Cosmology
• Astrophysics
• Data Analysis

Background:

• Cosmic Microwave Background (CMB) lensing is crucial for upcoming experiments like AdvACT, SPT-3G, and Simons Observatory.
• Temperature maps are vital for CMB lensing but suffer significant biases from foreground contamination.
• Existing methods like component separation and masking struggle to fully mitigate these foreground biases.

Purpose of the Study:

• To develop novel CMB lensing estimators that are robust against foreground contamination.
• To significantly reduce lensing biases in temperature maps, enhancing cosmological parameter estimation.
• To introduce new diagnostic tools for residual foregrounds in CMB lensing analysis.

Main Methods:

• Decomposing the standard CMB lensing quadratic estimator into optimal multipole estimators.
• Leveraging symmetry differences between lensed CMB and extragalactic foregrounds.
• Developing a novel method to compute primary, secondary, and trispectrum biases from simulations without noise.

Main Results:

• The new shear-only estimator demonstrates approximate immunity to extragalactic foregrounds, even in single-frequency maps.
• The shear estimator is insensitive to various foregrounds, including CIB, tSZ, kSZ, and radio point sources.
• The method allows inclusion of higher temperature multipoles, increasing the lensing signal-to-noise ratio beyond the standard quadratic estimator.

Conclusions:

• The developed multipole estimators offer a significant advancement in CMB lensing analysis, particularly for temperature-based measurements.
• The shear-only estimator provides a powerful tool to mitigate foreground biases, enabling more precise cosmological inference.
• Magnification-only and shear B-mode estimators serve as valuable diagnostics for assessing residual systematic errors.