Source Distributions of Cosmic Shear Surveys in Efficiency Space

Nicolas Tessore,Ian Harrison

doi:10.21105/astro.2003.11558

Abstract

We show that the lensing efficiency of cosmic shear generically has a simple shape, even in the case of a tomographic survey with badly behaved photometric redshifts. We argue that source distributions for cosmic shear can therefore be more effectively parametrised in "efficiency space". Using realistic simulations, we find that the true lensing efficiency of a current cosmic shear survey without disconnected outliers in the redshift distributions can be described to per cent accuracy with only two parameters, and the approach straightforwardly generalises to other parametric forms and surveys. The cosmic shear signal is thus largely insensitive to the details of the source distributions, and the features that matter can be summarised by a small number of suitable efficiency parameters. For the simulated survey, we show that prior knowledge at the ten per cent level, which is attainable e.g. from photometric redshifts, is enough to marginalise over the efficiency parameters without severely affecting the constraints on the cosmology parameters Ωm and σ8. A Jupyter notebook and associated files can be found <a href="https://github.com/cosmiclens/arXiv-2003.11558">here</a>. Open J. Astrophys. 3(2020) 6

Highlights

Measurements of cosmic shear obtained via the weak lensing effect on individual galaxy shapes are one of the best available probes of the late Universe where Dark Energy dominates
We find that the efficiency parameters μ and η suffice to describe a DES Y1-like cosmic shear survey
We have shown that the distribution of distances to sources in a cosmic shear analysis can be modelled directly in the space of the lensing efficiency, rather than in the space of the source redshifts

Summary

INTRODUCTION

Measurements of cosmic shear obtained via the weak lensing effect on individual galaxy shapes are one of the best available probes of the late Universe where Dark Energy dominates. A well-motivated and principled way of accounting for a much wider range of statistical uncertainties than the shift in mean involves marginalising over the heights of histogram bins for the number count of weak lensing source galaxies as a function of redshift (e.g. Leistedt et al 2016; Sanchez & Bernstein 2019; Alarcon et al 2019), but this necessarily creates a large number of new nuisance parameters

PARAMETRIC LENSING EFFICIENCY

COSMOLOGICAL PARAMETER INFERENCE

Findings

CONCLUSION