Cosmic convergence and shear with extended sources

TL;DR

This paper investigates how finite source sizes affect weak gravitational lensing measurements, finding that the infinitesimal-beam approximation remains valid for current data, with finite-beam effects being generally small.

Contribution

It provides a detailed analysis of finite-beam corrections in realistic cosmological models, clarifying their significance and validating the infinitesimal-beam approximation for current surveys.

Findings

Finite-beam corrections are subpercent in typical survey settings.

Percent-level corrections occur only at very small angular scales.

Previous overestimations of finite-beam effects are corrected by realistic matter distribution models.

Abstract

The standard theory of weak gravitational lensing relies on the approximation that light beams are infinitesimal. Our recent work showed that the finite size of sources, and the associated light beams, can cause nonperturbative corrections to the weak-lensing convergence and shear. This article thoroughly investigates these corrections in a realistic cosmological model. The continuous transition from infinitesimal to finite beams is understood, and reveals that the previous results overestimated finite-beam effects due to simplistic assumptions on the distribution of matter in the Universe. In a KiloDegree Survey-like setting, finite-beam corrections to the cosmic shear remain subpercent, while percent-level corrections are only reached on subarcmin scales. This article thus demonstrates the validity of the infinitesimal-beam approximation in the interpretation of current weak-lensing data.