The completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: 1000 multi-tracer mock catalogues with redshift evolution and systematics for galaxies and quasars of the final data release

TL;DR

The paper tackles the need for robust covariance estimates in BAO and RSD analyses using the final eBOSS DR16 data by generating 1000 EZmock realizations per tracer type (LRG, ELG, QSO) over 0.6 < z < 2.2. It advances a fast, ZA-based mock framework with a calibrated effective bias model, incorporating redshift evolution, light-cone construction, and observational systematics to reproduce two- and three-point clustering statistics and cross-tracer covariances. The results show that auto- and cross-clustering statistics from EZmocks agree with data within ~1σ in configuration space and up to 0.3 h Mpc^-1 in Fourier space, validating the mocks for covariance estimation, with some modeled limitations at small scales or high-k cross-correlations. The final publicly available EZmock catalogs provide a practical, scalable resource for multi-tracer cosmological analyses of eBOSS DR16, enabling reliable inference of BAO, RSD, and growth-rate measurements across tracers.

Abstract

We produce 1000 realizations of synthetic clustering catalogues for each type of the tracers used for the baryon acoustic oscillation and redshift space distortion analysis of the Sloan Digital Sky Surveys-IV extended Baryon Oscillation Spectroscopic Survey final data release (eBOSS DR16), covering the redshift range from 0.6 to 2.2, to provide reliable estimates of covariance matrices and test the robustness of the analysis pipeline with respect to observational systematics. By extending the Zel'dovich approximation density field with an effective tracer bias model calibrated with the clustering measurements from the observational data, we accurately reproduce the two- and three-point clustering statistics of the eBOSS DR16 tracers, including their cross-correlations in redshift space with very low computational costs. In addition, we include the gravitational evolution of structures and sample selection biases at different redshifts, as well as various photometric and spectroscopic systematic effects. The agreements on the auto-clustering statistics between the data and mocks are generally within 1 $σ$ variances inferred from the mocks, for scales down to a few $h^{-1}\,{\rm Mpc}$ in configuration space, and up to $0.3\,h\,{\rm Mpc}^{-1}$ in Fourier space. For the cross correlations between different tracers, the same level of consistency presents in configuration space, while there are only discrepancies in Fourier space for scales above $0.15\,h\,{\rm Mpc}^{-1}$. The accurate reproduction of the data clustering statistics permits reliable covariances for multi-tracer analysis.

Figures (22)

• Figure 1: The sky coverage of eBOSS DR16 tracers and BOSS DR12 LRGs, as well as the density map of Gaia DR2 sources with $g < 15\,{\rm mag}$.
• Figure 2: The weighted comoving number densities of eBOSS DR16 tracers and BOSS DR12 CMASS LRGs, with all the photometric and spectroscopic systematic weights included. The comoving distances and volumes are evaluated in the flat $\Lambda$CDM cosmology with $\Omega_{\rm m} = 0.31$. The three horizontal dashed lines show the number densities of the cubic LRG, ELG, and QSO EZmock catalogues, i.e. $3.2 \times 10^{-4}$, $6.4 \times 10^{-4}$, and $2.4 \times 10^{-5}\,h^3\,{\rm Mpc}^{-3}$, respectively.
• Figure 3: The comoving volume of EZmock catalogues after survey volume trimming, compared with the $(5\,h^{-1}\,{\rm Gpc})^3$ periodic box for constructing the mocks. Regions with different colours indicate the redshift slices used for reproducing the redshift evolution of clustering statistics (see Section \ref{['sec:ezmock_zbin']}). The QSO sample in the NGC benefits from the periodic boundary conditions, as its comoving volume is too large to be placed inside the box.
• Figure 4: Angular veto masks for eBOSS DR16 tracers and BOSS DR12 CMASS LRGs, for the same patch of the sky. Tracers in the coloured regions are removed for various reasons, such as bright source contaminations or unreliable photometric measurements.
• Figure 5: (Weighted) tracer distribution of the BOSS/eBOSS data and EZmock catalogues, normalized by the number of objects in the corresponding data catalogues. 'EZmock comp.' and 'EZmock syst.' denote the complete and realistic EZmock catalogues respectively, and 'wt.' indicates results evaluated with weights, which are the total photometric and spectroscopic weights used for clustering analyses. The upper and lower boundaries of the filled regions show the 1 $\sigma$ deviation obtained from 1000 realizations of mocks.