Abstract
ABSTRACTUpcoming surveys will use a variety of galaxy selections to map the large-scale structure of the Universe. It is important to make accurate predictions for the properties and clustering of such galaxies, including the errors on these statistics. Here, we describe a novel technique which uses the semi-analytical model of galaxy formation galform, embedded in the high-resolution N-body Planck-Millennium simulation, to populate a thousand halo catalogues generated using the Parallel-PM N-body glam code. Our hybrid scheme allows us to make clustering predictions on scales that cannot be modelled in the original N-body simulation. We focus on luminous red galaxies (LRGs) selected in the redshift range z = 0.6 − 1 from the galform output using similar colour-magnitude cuts in the r, z, and W1 bands to those that will be applied in the Dark Energy Spectroscopic Instrument (DESI) survey, and call this illustrative sample ‘DESI-like’ LRGs. We find that the LRG-halo connection is non-trivial, leading to the prediction of a non-standard halo occupation distribution; in particular, the occupation of central galaxies does not reach unity for the most massive haloes, and drops with increasing mass. The glam catalogues reproduce the abundance and clustering of the LRGs predicted by galform. We use the glam mocks to compute the covariance matrices for the two-point correlation function and power spectrum of the LRGs and their background dark matter density field, revealing important differences. We also make predictions for the linear-growth rate and the baryon acoustic oscillations distances at z = 0.6, 0.74, and 0.93. All ‘DESI-like’ LRG catalogues are made publicly available.
Highlights
Luminous red galaxies (LRGs) display a strong clustering signal, thanks to their bright intrinsic luminosity and large stellar masses, that makes them an ideal tracer of the large-scale structure of the Universe (Eisenstein et al 2005a; Zehavi et al 2005)
There are a number of differences between the work carried out by Zhou et al (2020a) and our paper: first, we are interested in providing a study of the impact of the Dark Energy Spectroscopic Instrument (DESI)-luminous red galaxies (LRGs) target selection on galaxy properties and the galaxy-halo connection using a physical model of galaxy formation, GALFORM; and secondly, we focus on the large-scale galaxy clustering and in the generation of a large number of mock catalogues to provide an accurate estimate of the covariance of the clustering measurements
In order to match local observations of galaxies, just two of the parameters describing the physical processes modelled in GALFORM were changed slightly by Baugh et al, from the values adopted by Gonzalez-Perez et al, to take into account the change in cosmology and mass resolution in the PMILL compared with the original N-body simulation used by Gonzalez-Perez et al, and an improvement to the treatment of galaxy mergers
Summary
Luminous red galaxies (LRGs) display a strong clustering signal, thanks to their bright intrinsic luminosity and large stellar masses, that makes them an ideal tracer of the large-scale structure of the Universe (Eisenstein et al 2005a; Zehavi et al 2005). There are a number of differences between the work carried out by Zhou et al (2020a) and our paper: first, we are interested in providing a study of the impact of the DESI-LRG target selection on galaxy properties and the galaxy-halo connection using a physical model of galaxy formation, GALFORM; and secondly, we focus on the large-scale galaxy clustering and in the generation of a large number of mock catalogues to provide an accurate estimate of the covariance of the clustering measurements Both of these objectives are beyond the reach of the original simulation used to run the SAM and mark a key advantage of our hybrid approach. Our aim is to illustrate our approach using a sample that approximates to DESI LRGs
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