DESI mock challenge

Abstract

Context. We present a novel approach to the construction of mock galaxy catalogues for large-scale structure analysis based on the distribution of dark matter halos obtained with effective bias models at the field level. Aims. We aim to produce mock galaxy catalogues capable of generating accurate covariance matrices for a number of cosmological probes that are expected to be measured in current and forthcoming galaxy redshift surveys (e.g. two- and three-point statistics). The construction of the catalogues shown in this paper is part of a mock-comparison project within the Dark Energy Spectroscopic Instrument (DESI) collaboration. Methods. We use the bias assignment method (BAM) to model the statistics of halo distribution through a learning algorithm using a few detailed N-body simulations, and approximated gravity solvers based on Lagrangian perturbation theory. We introduce cosmic-web-dependent corrections to modelling redshift-space distortions at the N-body level – both in the halo and galaxy distributions –, as well as a multi-scale approach for accurate assignment of halo properties. Using specific models of halo occupation distributions to populate halos, we generate galaxy mocks with the expected number density and central-satellite fraction of emission-line galaxies, which are a key target of the DESI experiment. Results. BAM generates mock catalogues with per cent accuracy in a number of summary statistics, such as the abundance, the two- and three-point statistics of halo distributions, both in real and redshift space. In particular, the mock galaxy catalogues display ∼3%−10% accuracy in the multipoles of the power spectrum up to scales of k ∼ 0.4 h−1Mpc. We show that covariance matrices of two- and three-point statistics obtained with BAM display a similar structure to the reference simulation. Conclusions. BAM offers an efficient way to produce mock halo catalogues with accurate two- and three-point statistics, and is able to generate a variety of multi-tracer catalogues with precise covariance matrices of several cosmological probes. We discuss future developments of the algorithm towards mock production in DESI and other galaxy-redshift surveys.

Validation of the Scientific Program for the Dark Energy Spectroscopic Instrument

“…A series of numerical simulations have been compared at the halo level to assess the robustness of numerical simulation methods (Grove et al 2022), while new techniques have been developed to suppress the effects of sample variance in these N-body simulations using approximate mocks (Ding et al 2022). New high-fidelity mock galaxy catalogs have also been developed with mass resolution sufficient to resolve dark matter subhaloes for the BGS sample (Safonova et al 2021), while various techniques have been developed to produce mock catalogs over volumes much larger than possible with N-body simulations (Balaguera-Antolínez et al 2023).…”

The cosmic web from perturbation theory

“…While EZmocks relies on the Zel'dovich approximation (Zel'dovich 1970), PATCHY and BAM rely on ALPT, including tidal field corrections (Kitaura & Hess 2013). It has been shown that such methods can, to a great extent, correct the bias introduced by approximate gravity solvers in the nonlinear and non-local bias description (see the application of BAM to galaxy catalogues, Balaguera-Antolínez et al 2023).…”