Validating galaxy clustering models with fixed and paired and matched-ICs simulations: application to primordial non-Gaussianities

Abstract

The Fix and Pair techniques were designed to generate simulations with reduced variance in the 2-point statistics by modifying the Initial Conditions (ICs). In this paper we show that this technique is also valid when the initial conditions have local Primordial non-Gaussianities (PNG), parametrised by fNL, without biasing the 2-point statistics but reducing significantly their variance. We show how to quantitatively use these techniques to test the accuracy of galaxy/halo clustering models down to a much reduced uncertainty and we apply them to test the standard model for halo clustering in the presence of PNG. Additionally, we show that by Matching the stochastic part of the ICs for two different cosmologies (Gaussian and non-Gaussian) we obtain a large correlation between the (2-point) statistics that can explicitly be used to further reduce the uncertainty of the model testing. For our reference analysis (fNL = 100, V = 1[h−1Gpc]3, n = 2.5 × 10−4[h−1Mpc]−3, b = 2.32), we obtain an uncertainty of σ(fNL) = 60 with a standard simulation, whereas using Fixed [Fixed-Paired] initial conditions it reduces to σ(fNL) = 12 [σ(fNL) = 12]. When also Matching the ICs we obtain σ(fNL) = 18 for the standard case, and σ(fNL) = 8 [σ(fNL) = 7] for Fixed [Fixed-Paired]. The combination of the Fix, Pair and Match techniques can be used in the context of PNG to create simulations with an effective volume incremented by a factor ∼70 at given computational resources.

Primordial non-Gaussianity with angular correlation function: integral constraint and validation for DES

“…8 Subsequently, the z = 1 dark matter snapshots are run through the Amiga Halo Finder 9 to construct the halo catalogues with a minimum of 10 particles, which yield M h ∼ 5 × 10 12 M as the halo mass resolution. Also, for the GOLIAT-PNG simulations, it was found that p = 0.90 for f NL = 100 (Avila & Adame 2023 ), and p = 0.92 for f NL = −100, when measuring their real space power spectra, and we will consider this when measuring f NL from these mocks.…”

“…Another particularity of these simulations is that the initial conditions are run with the fixed and paired initial conditions (Angulo & Pontzen 2016 ) aimed at reducing the sample variance of the ensemble average of the two-point functions measured from these simulations. In the context of PNG, this technique is validated in Avila & Adame ( 2023 ), and we refer the reader there for further details of the GOLIAT-PNG suite. We use 41 pairs of simulations for each value of f NL .…”

“…The methods are analysed for two kinds of simulations. First, we introduce the GOLIAT-PNG mocks (Avila & Adame 2023 ), a set of 246 N -Body simulations that have non-Gaussian initial conditions. We use these simulations to remark on the importance of the IC when measuring f loc NL .…”