The Accuracy of Weak Lensing Simulations

TL;DR

This study compares five independent weak lensing simulation codes on the same data, finding high agreement in convergence maps and quantifying systematic errors, thus validating their accuracy for cosmological analyses.

Contribution

It provides a detailed comparison of multiple lensing simulation codes, assessing their accuracy and systematic errors, which is crucial for reliable cosmological inferences.

Findings

Convergence power spectra agree within 2% up to a0 ilde{a0} a0 ildea0 4000 in multipole a0 ildea0 a0 ildea0

Peak counts agree within 5% for peaks with S/N a0 ildea0 a0 ildea0 6

Systematic errors from simulation methods are small and predictable

Abstract

We investigate the accuracy of weak lensing simulations by comparing the results of five independently developed lensing simulation codes run on the same input $N$-body simulation. Our comparison focuses on the lensing convergence maps produced by the codes, and in particular on the corresponding PDFs, power spectra and peak counts. We find that the convergence power spectra of the lensing codes agree to $\lesssim 2\%$ out to scales $\ell \approx 4000$. For lensing peak counts, the agreement is better than $5\%$ for peaks with signal-to-noise $\lesssim 6$. We also discuss the systematic errors due to the Born approximation, line-of-sight discretization, particle noise and smoothing. The lensing codes tested deal in markedly different ways with these effects, but they nonetheless display a satisfactory level of agreement. Our results thus suggest that systematic errors due to the operation of existing lensing codes should be small. Moreover their impact on the convergence power spectra for a lensing simulation can be predicted given its numerical details, which may then serve as a validation test.