Measuring the scale dependence of intrinsic alignments using multiple shear estimates

TL;DR

This paper introduces a novel method leveraging multiple shear estimates on the same galaxy sample to enhance the measurement of the scale dependence of intrinsic alignments, improving signal-to-noise ratio over previous techniques.

Contribution

The paper presents a new approach that exploits correlations between different shear estimates to better measure intrinsic alignments in galaxy-galaxy lensing.

Findings

Signal-to-noise ratio improved by a factor of ~2 using the new method.

Statistical error dominates the intrinsic alignment measurement.

Extension of previous methods increases measurement sensitivity.

Abstract

We present a new method for measuring the scale dependence of the intrinsic alignment (IA) contamination to the galaxy-galaxy lensing signal, which takes advantage of multiple shear estimation methods applied to the same source galaxy sample. By exploiting the resulting correlation of both shape noise and cosmic variance, our method can provide an increase in the signal-to-noise of the measured IA signal as compared to methods which rely on the difference of the lensing signal from multiple photometric redshift bins. For a galaxy-galaxy lensing measurement which uses LSST sources and DESI lenses, the signal-to-noise on the IA signal from our method is predicted to improve by a factor of $\sim 2$ relative to the method of Blazek et al. 2012, for pairs of shear estimates which yield substantially different measured IA amplitudes and highly correlated shape noise terms. We show that statistical error necessarily dominates the measurement of intrinsic alignments using our method. We also consider a physically motivated extension of the Blazek et al. 2012 method which assumes that all nearby galaxy pairs, rather than only excess pairs, are subject to IA. In this case, the signal-to-noise of the method of Blazek et al. 2012 is improved.