Weak lensing peak statistics in the era of large scale cosmological surveys

TL;DR

This paper assesses the use of fast COLA simulations for predicting weak lensing peak counts in large surveys, demonstrating their accuracy and exploring optimal data configurations for improved cosmological constraints.

Contribution

It introduces the application of COLA simulations coupled with Ufalcon for weak lensing peak prediction and evaluates their systematic errors relative to full simulations.

Findings

COLA method's systematic errors are smaller than statistical errors for 2000 deg$^2$ surveys.

Combining multiple smoothing scales significantly enhances constraining power.

Tomography adds limited improvement compared to smoothing scale combination.

Abstract

Weak lensing peak counts are a powerful statistical tool for constraining cosmological parameters. So far, this method has been applied only to surveys with relatively small areas, up to several hundred square degrees. As future surveys will provide weak lensing datasets with size of thousands of square degrees, the demand on the theoretical prediction of the peak statistics will become heightened. In particular, large simulations of increased cosmological volume are required. In this work, we investigate the possibility of using simulations generated with the fast Comoving-Lagrangian acceleration (COLA) method, coupled to the convergence map generator Ufalcon, for predicting the peak counts. We examine the systematics introduced by the COLA method by comparing it with a full TreePM code. We find that for a 2000 deg$^2$ survey, the systematic error is much smaller than the statistical error. This suggests that the COLA method is able to generate promising theoretical predictions for weak lensing peaks. We also examine the constraining power of various configurations of data vectors, exploring the influence of splitting the sample into tomographic bins and combining different smoothing scales. We find the combination of smoothing scales to have the most constraining power, improving the constraints on the $S_8$ amplitude parameter by at least 40% compared to a single smoothing scale, with tomography brining only limited increase in measurement precision.