The DESI N-body Simulation Project-II. Suppressing sample variance with fast simulations

Zhejie Ding*, Chia Hsun Chuang*, Yu Yu*, Lehman H. Garrison, Adrian E. Bayer, Yu Feng, Chirag Modi, Daniel J. Eisenstein, Martin White, Andrei Variu, Cheng Zhao, Hanyu Zhang, Jennifer Meneses Rizo, David Brooks, Kyle Dawson, Peter Doel, Enrique Gaztanaga, Robert Kehoe, Alex Krolewski, Martin LandriauNathalie Palanque-Delabrouille, Claire Poppett

*Corresponding author for this work

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Dark Energy Spectroscopic Instrument (DESI) will construct a large and precise three-dimensional map of our Universe. The survey effective volume reaches ∼ 20 h-3, Gpc3. It is a great challenge to prepare high-resolution simulations with a much larger volume for validating the DESI analysis pipelines. AbacusSummit is a suite of high-resolution dark-matter-only simulations designed for this purpose, with 200,-3}, Gpc3 (10 times DESI volume) for the base cosmology. However, further efforts need to be done to provide a more precise analysis of the data and to cover also other cosmologies. Recently, the CARPool method was proposed to use paired accurate and approximate simulations to achieve high statistical precision with a limited number of high-resolution simulations. Relying on this technique, we propose to use fast quasi-N-body solvers combined with accurate simulations to produce accurate summary statistics. This enables us to obtain 100 times smaller variance than the expected DESI statistical variance at the scales we are interested in, e.g. k < 0.3h Mpc-1 for the halo power spectrum. In addition, it can significantly suppress the sample variance of the halo bispectrum. We further generalize the method for other cosmologies with only one realization in AbacusSummit suite to extend the effective volume ∼20 times. In summary, our proposed strategy of combining high-fidelity simulations with fast approximate gravity solvers and a series of variance suppression techniques sets the path for a robust cosmological analysis of galaxy survey data.

Original languageEnglish
Pages (from-to)3308-3328
Number of pages21
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Early online date2 Jun 2022
Publication statusPublished - 1 Aug 2022


  • cosmology: theory
  • galaxies: haloes
  • large-scale structure of Universe
  • methods: statistical
  • UKRI
  • STFC

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