The DESI DR1 Peculiar Velocity Survey: Mock Catalog

TL;DR

This work delivers the official DESI DR1 Peculiar Velocity mock catalogs, built from AbacusSummit N-body simulations with a nested-HOD galaxy model to reproduce the DESI BGS density and clustering and to generate FP, TF, and SN distance indicators. The 675 cut-sky realizations enable rigorous, cross-method validation of PV growth-rate measurements and accurate covariance estimation for three analytic approaches (MLE, momentum power spectra, and velocity–density cross-correlations). The authors compute a consensus growth-rate result, $f\sigma_8 = 0.450 \pm 0.055$, demonstrating consistency with General Relativity and $\Lambda$CDM at low redshift and highlighting the mocks' role in uncertainty quantification and methodology cross-calibration. This mock suite represents the largest and most realistic set of peculiar-velocity mocks to date, with broad implications for future DESI DR2/DR3 analyses and PV-based tests of gravity and dark energy.

Abstract

We describe the production of the official set of mock catalogs for the Dark Energy Spectroscopic Instrument Peculiar Velocity Survey (DESI-PV) Data Release 1 (DR1). Our mock catalogs reproduce the Bright Galaxy Survey number density and clustering at low redshift $(z<0.1)$ and the DESI PV samples of Fundamental plane and Tully-Fisher distances, from which we derive peculiar velocities. We carefully match mock and data properties and we mimic measurements of distance indicators and peculiar velocities, which follow the same statistical properties as real data. Mock samples of type-Ia supernovae also complement the other two distance indicators. Our 675 available mock realizations were used consistently by our three different methodologies described in our companion papers that measure the growth rate of structure $fσ_8$ with DESI PV DR1. Those mocks allow us to perform precise tests of clustering models and uncertainty estimation to an unprecedented level of accuracy, and compute correlations between methodologies. The consensus value for the DESI DR1 PV growth rate measurement is $fσ_8 = 0.450 \pm 0.055$. This sample of mock catalogs represents the largest and most realistic set for cosmological measurements with peculiar velocities to date.

Figures (12)

• Figure 1: DESI DR1 sky coverage of mock BGS galaxies with color indicating spectroscopic completeness.
• Figure 2: Example comparisons between DESI BGS data and the base AbacusSummit mock catalogs. The left panel shows the $r$-band absolute magnitude against $g-r$ color, while the right panel shows the stellar mass against specific star formation rate. In both cases, the contours show the average properties over 27 simulations, with dark contours indicating regions of higher density. The colormap provides the number of real DESI galaxies in each bin, with light colours indicating higher density. For the purposes of this comparison, we restrict the DESI data to only those galaxies with $z<0.11$ and apparent magnitude $r<19.7$, consistent with the simulations.
• Figure 3: The number density versus redshift of DESI BGS galaxies in the density-field sample compared to a sample mock catalog, before and after applying a luminosity cut.
• Figure 4: The number density versus redshift of Fundamental Plane galaxies in the data compared to the average of 675 mocks, before (dotted) and after (solid line) a subsampling correction is applied to ensure the mocks match the expected number of galaxies. The error bars are derived from the standard deviation of over the 675 mocks and used to express the expected uncertainty on the data.
• Figure 5: Distribution of Fundamental Plane input parameters (effective radius $r$, velocity dispersion $s$ and surface brightness $i$) and their uncertainties for both the DESI FP data and averaged over 625 FP mock catalogs.