Efficiently estimating mean, uncertainty and unconstrained large scale fraction of local Universe simulations with paired fixed fields

TL;DR

This paper introduces an efficient method using paired fixed fields to estimate uncertainties and improve local Universe simulations, significantly reducing computational costs while maintaining accuracy.

Contribution

It adapts paired fixed field techniques to local Universe simulations, enabling rapid uncertainty estimation and more accurate modeling of large-scale cosmic structures.

Findings

Only 20% of large-scale power spectrum is purely random.

Paired fixed fields provide nearly unbiased average realizations.

Uncertainty can be estimated from just two simulations.

Abstract

Provided a random realization of the cosmological model, observations of our cosmic neighborhood now allow us to build simulations of the latter down to the non-linear threshold. The resulting local Universe models are thus accurate up to a given residual cosmic variance. Namely some regions and scales are apparently not constrained by the data and seem purely random. Drawing conclusions together with their uncertainties involves then statistics implying a considerable amount of computing time. By applying the constraining algorithm to paired fixed fields, this paper diverts the original techniques from their first use to efficiently disentangle and estimate uncertainties on local Universe simulations obtained with random fields. Paired fixed fields differ from random realizations in the sense that their Fourier mode amplitudes are fixed and they are exactly out of phase. Constrained paired fixed fields show that only 20% of the power spectrum on large scales (> tens of megaparsecs) is purely random. Namely 80% of it is partly constrained by the large scale / small scale data correlations. Additionally, two realizations of our local environment obtained with paired fixed fields of the same pair constitute an excellent non-biased average or quasi-linear realization of the latter, namely the equivalent of hundreds of constrained simulations. The variance between these two realizations gives the uncertainty on the achievable local Universe simulations. These two simulations will permit enhancing faster our local cosmic web understanding thanks to a drastically reduced required computational time to appreciate its modeling limits and uncertainties.