Self-Calibration for 3-point Intrinsic Alignment Auto-Correlations in Weak Lensing Surveys

TL;DR

This paper proposes a self-calibration method for intrinsic alignment auto-correlations at the 3-point level in weak lensing surveys, leveraging redshift dependence to reduce contamination without relying on specific IA models.

Contribution

It introduces a novel 3-point self-calibration technique for intrinsic alignments based on redshift dependence, enhancing weak lensing measurement accuracy.

Findings

Future surveys can measure IA redshift dependence over |Δz^P| ≤ 0.2

The 3-point self-calibration achieves accuracy comparable to 2-point methods

Significantly reduces IA contamination in weak lensing bispectrum

Abstract

The weak lensing signal (cosmic shear) has been shown to be strongly contaminated by the various types of galaxy intrinsic alignment (IA) correlations, which poses a barrier to precision weak lensing measurements. The redshift dependence of the IA signal has been used at the 2-point level to reduce this contamination by only measuring cross-correlations between large redshift bins, which significantly reduces the galaxy intrinsic ellipticity - intrinsic ellipticity (II) correlation. A self-calibration technique based on the redshift dependences of the IA correlations has also been proposed as a means to remove the 2-point IA contamination from the lensing signal. We explore here the redshift dependences of the IA and lensing bispectra in order to propose a self-calibration of the IA auto-correlations at the 3-point level (i.e. GGI, GII, and III), which can be well understood without the assumption of any particular IA model. We find that future weak lensing surveys will be able to measure the distinctive IA redshift dependence over ranges of $|\Delta z^P|\le 0.2$. Using conservative estimates of photo-z accuracy, we describe the 3-point self-calibration technique for the total IA signal, which can be accomplished through lensing tomography of photo-z bin size $\sim 0.01$. We find that the 3-point self-calibration can function at the accuracy of the 2-point technique with modest constraints in redshift separation. This allows the 3-point IA auto-correlation self-calibration technique proposed here to significantly reduce the contamination of the IA contamination to the weak lensing bispectrum.