The density distributions of cosmic structures: impact of the local environment on weak-lensing convergence

TL;DR

This paper investigates how local environmental effects influence weak-lensing observations and cosmological parameter constraints, using relativistic N-body simulations and ray-tracing to understand the impact on large-scale structure measurements.

Contribution

It introduces a numerical framework combining null geodesic solutions and ray-tracing to quantify local environment effects on weak-lensing statistics in relativistic simulations.

Findings

Local environment significantly affects weak-lensing convergence at low redshifts.

The minimal redshift for reliable cosmological parameter constraints is approximately 0.2 for 0 and 0.6 for H0.

Beyond these redshifts, local effects become negligible, improving the robustness of WL survey data.

Abstract

Whilst the underlying assumption of the Friedman-Lema\^itre-Robertson-Walker (FLRW) cosmological model is that matter is homogeneously distributed throughout the universe, gravitational influences over the life of the universe have resulted in mass clustered on a range of scales. Hence we expect that, in our inhomogeneous universe, the view of an observer will be influenced by the location and local environment. Here we analyse the one-point probability distribution functions and angular power spectra of weak-lensing (WL) convergence and magnification numerically to investigate the influence of our local environment on WL statistics in relativistic $N$-body simulations. To achieve this, we numerically solve the null geodesic equations which describe the propagation of light bundles backwards in time from today, and develop a ray-tracing algorithm, and from these calculate various WL properties. Our findings demonstrate how cosmological observations of large-scale structure through WL can be impacted by the locality of the observer. We also calculate the constraints on the cosmological parameters as a function of redshift from the theoretical and numerical study of the angular power spectrum of WL convergence. This study concludes the minimal redshift for the constraint on the parameter $\Omega_m$ ($H_0$) is $z \sim 0.2$ $(z \sim 0.6 )$ beyond which the local environment's effect is negligible and the data from WL surveys are more meaningful above that redshift. The outcomes of this study will have direct consequences for future surveys, where percent-level-precision is necessary.