Sources of contamination to weak lensing tomography: redshift-dependent shear measurement bias

TL;DR

This paper investigates how redshift-dependent shear measurement biases, specifically from KSB methods, impact weak lensing tomography and cosmological parameter estimation, emphasizing the necessity to account for such biases in future analyses.

Contribution

It quantifies the effect of redshift-dependent shear measurement bias on weak lensing tomography and provides a framework for marginalizing over this bias in cosmological parameter estimation.

Findings

Biased aperture mass dispersion reduces by ~20% at redshift ~1.

Ignoring bias leads to a few percent error in sigma_8 and w_0 estimates.

Tomography constraints degrade significantly when marginalizing over shape measurement biases.

Abstract

The current methods available to estimate gravitational shear from astronomical images of galaxies introduce systematic errors which can affect the accuracy of weak lensing cosmological constraints. We study the impact of KSB shape measurement bias on the cosmological interpretation of tomographic two-point weak lensing shear statistics. We use a set of realistic image simulations produced by the STEP collaboration to derive shape measurement bias as a function of redshift. We define biased two-point weak lensing statistics and perform a likelihood analysis for two fiducial surveys. We present a derivation of the covariance matrix for tomography in real space and a fitting formula to calibrate it for non-Gaussianity. We find the biased aperture mass dispersion is reduced by ~20% at redshift ~1, and has a shallower scaling with redshift. This effect, if ignored in data analyses, biases sigma_8 and w_0 estimates by a few percent. The power of tomography is significantly reduced when marginalising over a range of realistic shape measurement biases. For a CFHTLS-Wide-like survey, [Omega_m, sigma_8] confidence regions are degraded by a factor of 2, whereas for a KIDS-like survey the factor is 3.5. Our results are strictly valid only for KSB methods but they demonstrate the need to marginalise over a redshift-dependent shape measurement bias in all future cosmological analyses.