Source-lens clustering and intrinsic-alignment bias of weak-lensing estimators

TL;DR

This paper quantifies the source-lens clustering and intrinsic-alignment biases in weak lensing estimators, showing they can significantly affect three-point correlation measurements and must be considered for high-precision cosmology.

Contribution

It provides a detailed estimation of these biases using analytical models, highlighting their importance for accurate weak lensing analysis.

Findings

Source-lens clustering bias is negligible except for very low-redshift correlations.

Intrinsic-alignment bias is about 10% of the signal for two- and three-point statistics.

Biases can reach 10% or more, affecting precision measurements.

Abstract

We estimate the amplitude of the source-lens clustering bias and of the intrinsic-alignment bias of weak lensing estimators of the two-point and three-point convergence and cosmic-shear correlation functions. We use a linear galaxy bias model for the galaxy-density correlations, as well as a linear intrinsic-alignment model. For the three-point and four-point density correlations, we use analytical or semi-analytical models, based on a hierarchical ansatz or a combination of one-loop perturbation theory with a halo model. For two-point statistics, we find that the source-lens clustering bias is typically several orders of magnitude below the weak lensing signal, except when we correlate a very low-redshift galaxy ($z_2 \la 0.05$) with a higher redshift galaxy ($z_1 \ga 0.5$), where it can reach $10\%$ of the signal for the shear. For three-point statistics, the source-lens clustering bias is typically of order $10\%$ of the signal, as soon as the three galaxy source redshifts are not identical. The intrinsic-alignment bias is typically about $10\%$ of the signal for both two-point and three-point statistics. Thus, both source-lens clustering bias and intrinsic-alignment bias must be taken into account for three-point estimators aiming at a better than $10\%$ accuracy.