Propagating residual biases in masked cosmic shear power spectra

TL;DR

This paper derives how residual biases in weak lensing measurements propagate into cosmic shear power spectra, highlighting the importance of priors and bias control for accurate cosmological inference.

Contribution

It provides a full expression for bias propagation, shows higher-order terms are negligible, and identifies B-mode power as a bias indicator, advancing understanding of bias impacts in cosmic shear analysis.

Findings

Higher-order bias terms are negligible.

B-mode power contains information on multiplicative bias.

Accurate constraints require priors on bias and ellipticity variance.

Abstract

In this paper we derive a full expression for the propagation of weak lensing shape measurement biases into cosmic shear power spectra including the effect of missing data. We show using simulations that terms higher than first order in bias parameters can be ignored and the impact of biases can be captured by terms dependent only on the mean of the multiplicative bias field. We identify that the B-mode power contains information on the multiplicative bias. We find that without priors on the residual multiplicative bias $\delta m$ and stochastic ellipticity variance $\sigma_e$ that constraints on the amplitude of the cosmic shear power spectrum are completely degenerate, and that when applying priors the constrained amplitude $A$ is slightly biased low via a classic marginalisation paradox. Using all-sky Gaussian random field simulations we find that the combination of $(1+2\delta m)A$ is unbiased for a joint EE and BB power spectrum likelihood if the error and mean (precision and accuracy) of the stochastic ellipticity variance is known to better than $\sigma(\sigma_e)\leq 0.05$ and $\Delta\sigma_e\leq 0.01$, or the multiplicative bias is known to better than $\sigma(m)\leq 0.07$ and $\Delta m\leq 0.01$.