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The DESI N-body simulation project – I. Testing the robustness of simulations for the DESI dark time survey

Grove, Cameron; Chuang, Chia-Hsun; Devi, Ningombam Chandrachani; Garrison, Lehman; L’Huillier, Benjamin; Feng, Yu; Helly, John; Hernández-Aguayo, César; Alam, Shadab; Zhang, Hanyu; Yu, Yu; Cole, Shaun; Eisenstein, Daniel; Norberg, Peder; Wechsler, Risa; Brooks, David; Dawson, Kyle; Landriau, Martin; Meisner, Aaron; Poppett, Claire; Tarlé, Gregory; Valenzuela, Octavio

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Chia-Hsun Chuang

Ningombam Chandrachani Devi

Lehman Garrison

Benjamin L’Huillier

Yu Feng

César Hernández-Aguayo

Shadab Alam

Hanyu Zhang

Yu Yu

Daniel Eisenstein

Risa Wechsler

David Brooks

Kyle Dawson

Martin Landriau

Aaron Meisner

Claire Poppett

Gregory Tarlé

Octavio Valenzuela


Analysis of large galaxy surveys requires confidence in the robustness of numerical simulation methods. The simulations are used to construct mock galaxy catalogues to validate data analysis pipelines and identify potential systematics. We compare three N-body simulation codes, ABACUS, GADGET-2, and SWIFT, to investigate the regimes in which their results agree. We run N-body simulations at three different mass resolutions, 6.25 × 108, 2.11 × 109, and 5.00 × 109 h−1 M, matching phases to reduce the noise within the comparisons. We find systematic errors in the halo clustering between different codes are smaller than the Dark Energy Spectroscopic Instrument (DESI) statistical error for s > 20 h−1 Mpc in the correlation function in redshift space. Through the resolution comparison we find that simulations run with a mass resolution of 2.1 × 109 h−1 M are sufficiently converged for systematic effects in the halo clustering to be smaller than the DESI statistical error at scales larger than 20 h−1 Mpc. These findings show that the simulations are robust for extracting cosmological information from large scales which is the key goal of the DESI survey. Comparing matter power spectra, we find the codes agree to within 1 per cent for k ≤ 10 h Mpc−1. We also run a comparison of three initial condition generation codes and find good agreement. In addition, we include a quasi-N-body code, FastPM, since we plan use it for certain DESI analyses. The impact of the halo definition and galaxy–halo relation will be presented in a follow-up study.


Grove, C., Chuang, C., Devi, N. C., Garrison, L., L’Huillier, B., Feng, Y., …Valenzuela, O. (2022). The DESI N-body simulation project – I. Testing the robustness of simulations for the DESI dark time survey. Monthly Notices of the Royal Astronomical Society, 515(2),

Journal Article Type Article
Acceptance Date Jul 5, 2022
Online Publication Date Jul 22, 2022
Publication Date 2022
Deposit Date Aug 23, 2022
Publicly Available Date Aug 23, 2022
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 515
Issue 2


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Copyright Statement
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

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