Generating mock galaxy catalogues for flux-limited samples like the DESI Bright Galaxy Survey

TL;DR

This paper introduces a fast HOD-fitting method to generate accurate mock galaxy catalogues for flux-limited surveys like DESI BGS, validated against simulations and real data, and provides publicly available mocks across cosmologies.

Contribution

A novel, efficient HOD-fitting approach applied to large simulations to produce realistic mock galaxy catalogues for flux-limited surveys, including validation and public data release.

Findings

HOD fitting accurately reproduces galaxy clustering and densities

Mock catalogues show good agreement with DESI BGS measurements

Method is robust across different initial conditions and cosmologies

Abstract

Accurate mock galaxy catalogues are crucial to validate analysis pipelines used to constrain dark energy models. We present a fast HOD-fitting method which we apply to the AbacusSummit simulations to create a set of mock catalogues for the DESI Bright Galaxy Survey, which contain r-band magnitudes and g-r colours. The halo tabulation method fits HODs for different absolute magnitude threshold samples simultaneously, preventing unphysical HOD crossing between samples. We validate the HOD fitting procedure by fitting to real-space clustering measurements and galaxy number densities from the MXXL BGS mock, which was tuned to the SDSS and GAMA surveys. The best-fitting clustering measurements and number densities are mostly within the assumed errors, but the clustering for the faint samples is low on large scales. The best-fitting HOD parameters are robust when fitting to simulations with different realisations of the initial conditions. When varying the cosmology, trends are seen as a function of each cosmological parameter. We use the best-fitting HOD parameters to create cubic box and cut sky mocks from the AbacusSummit simulations, in a range of cosmologies. As an illustration, we compare the Mr<-20 sample of galaxies in the mock with BGS measurements from the DESI one-percent survey. We find good agreement in the number densities, and the projected correlation function is reasonable, with differences that can be improved in the future by fitting directly to BGS clustering measurements. The cubic box and cut-sky mocks in different cosmologies are made publicly available.