The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Large-scale Structure Catalogs for Cosmological Analysis

TL;DR

The paper presents the completed eBOSS DR16 large-scale structure catalogs for LRGs and quasars, including carefully constructed random catalogs and comprehensive corrections for observational systematics. It details the target selection, spectroscopic observing strategy, redshift estimation with the redrock/template approach, and a robust catalog creation pipeline that accounts for fiber collisions, veto masks, completeness, and imaging systematics. Key contributions include achieving high redshift success rates with quantified catastrophe rates, combining eBOSS LRGs with BOSS CMASS to form a large, uniform tracer sample, and providing randomized catalogs and weights optimized for BAO and RSD analyses. The catalogs, intended for cosmological analyses and public release, enable precise tests of cosmological models while ensuring systematics sub-dominant to statistical uncertainties and are complemented by mock catalogs and companion analyses. The work sets a benchmark for LSS data products and provides a foundation for DESI-era surveys to extend these capabilities.

Abstract

We present large-scale structure catalogs from the completed extended Baryon Oscillation Spectroscopic Survey (eBOSS). Derived from Sloan Digital Sky Survey (SDSS) -IV Data Release 16 (DR16), these catalogs provide the data samples, corrected for observational systematics, and random positions sampling the survey selection function. Combined, they allow large-scale clustering measurements suitable for testing cosmological models. We describe the methods used to create these catalogs for the eBOSS DR16 Luminous Red Galaxy (LRG) and Quasar samples. The quasar catalog contains 343,708 redshifts with $0.8 < z < 2.2$ over 4,808\,deg$^2$. We combine 174,816 eBOSS LRG redshifts over 4,242\,deg$^2$ in the redshift interval $0.6 < z < 1.0$ with SDSS-III BOSS LRGs in the same redshift range to produce a combined sample of 377,458 galaxy redshifts distributed over 9,493\,deg$^2$. Improved algorithms for estimating redshifts allow that 98 per cent of LRG observations result in a successful redshift, with less than one per cent catastrophic failures ($Δz > 1000$ ${\rm km~s}^{-1}$). For quasars, these rates are 95 and 2 per cent (with $Δz > 3000$ ${\rm km~s}^{-1}$). We apply corrections for trends between the number densities of our samples and the properties of the imaging and spectroscopic data. For example, the quasar catalog obtains a $χ^2$/DoF$= 776/10$ for a null test against imaging depth before corrections and a $χ^2$/DoF$=6/8$ after. The catalogs, combined with careful consideration of the details of their construction found here-in, allow companion papers to present cosmological results with negligible impact from observational systematic uncertainties.

Figures (11)

• Figure 1: The footprint of eBOSS targets. Black points show LRG and quasar targets that were tiled but did not obtain spectroscopic observations (see text). Yellow points show quasars that were observed. They almost entirely overlap the red points, which show LRGs that were observed. Blue points show 20 per cent of the ELGs that were observed. The gray points are BOSS CMASS galaxies from their LSS catalogs. The CMASS data has their veto masks applied, while no such masks are applied for the eBOSS data in this plot. The eBOSS LRG and quasar footprints with veto masks applied are shown in Section \ref{['sec:comp']} and the equivalent ELG footprint is shown in RaichoorELGcat.
• Figure 2: Left: The distribution of $\Delta v$ over 8,071 pairs of observations of the same LRG target at $0.6 < z < 1.0$ and with confident detections ($\Delta \chi^2 > 9$). $\Delta v$ is the difference in velocity between two redshift measurements of the same object. The solid line shows the best-fit Gaussian model to the distribution after requiring $|\Delta v| < 250$ km s$^{-1}$. The mean and dispersion are shown in the legend. Right: $\Delta v$ as a function of $\Delta \chi^2$, for 11,556 pairs where we apply no cut on redshift. $\Delta \chi^2$ represents the statistical difference between the best and the second best fit spectral template to a single spectrum. The lower $\Delta \chi^2$ in the pair is considered the independent parameter. Pairs in which one spectrum was fit with an archetype spectral template with negative amplitude are presented in red. The horizontal red dashed line shows the limit of $\Delta v = 1000$ km/s above which a pair is considered as a catastrophic failure. The dotted vertical line shows the $\Delta \chi^2=9$, below which results are classified as redshift failures.
• Figure 3: Histograms of the redshifts of samples used in eBOSS LSS analyses. The quasars are selected to pass our LSS sample target selection, as explained in the text, but many were already observed by previous generations of SDSS. The SDSS-III BOSS CMASS sample is included, as we combine this sample with eBOSS LRGs to produce one larger sample.
• Figure 4: The fraction of good quasar spectra as function of the square of spectrograph signal-to-noise in the $i$-band ($S_i$ in text; top panel) and as a function of the fiber ID (bottom panel). The vertical dotted line at fiber ID 500 denotes the split between spectrographs 1 and 2. The gray dashed lines display the result when not applying the $w_{\rm noz}$ weights that we determine based on these quantities, as described in the text.
• Figure 5: The fraction of good LRG spectra as function of the spectrograph signal to noise in the $i$-band (top panel) and as a function of the fiber ID (bottom panel). The gray dashed lines display the result when not applying the $w_{\rm noz}$ weights that we determine based on these quantities, as described in the text.