The Sixteenth Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra

TL;DR

This paper reports DR16, the sixteenth SDSS data release, highlighting the first APOGEE-2S southern data and the final eBOSS spectra release, TDSS completion, and SPIDERS VACs, while noting no new MaNGA data. It documents the data scope, access portals, and the APOGEE-2 data products (spectra, RVs, stellar parameters, and VACs) along with quality assessments and calibration updates. It also details the final eBOSS sample and VACs, including classifications and RM and SPIDERS products, and provides a forward-looking view toward SDSS-V and DR17. Overall, DR16 marks a culmination of SDSS-IV's cosmology and Milky Way programs, consolidates multi-hemisphere spectroscopic coverage, and expands value-added catalogs to enhance Galactic and extragalactic science, while laying groundwork for future surveys and open-data accessibility.

Abstract

This paper documents the sixteenth data release (DR16) from the Sloan Digital Sky Surveys; the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the southern hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey (TDSS) and new data from the SPectroscopic IDentification of ERosita Survey (SPIDERS) programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library "MaStar"). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17).

Figures (6)

• Figure 1: DR16 APOGEE sky coverage in Galactic coordinates. Each symbol represents a field, which is 7 square degrees for APOGEE-1 in cyan and APOGEE-2N in blue and 2.8 square degrees for APOGEE-2S in red (this difference is due to the different field-of-view of the two telescopes; see § \ref{['apogeeS']}). Fields that have new data presented in DR16 are hi-lighted with a black outline.
• Figure 2: A sky map in Galactic coordinates showing the number of stars per APOGEE field (across APOGEE-1, 2N, and 2S). The disk is targeted with a symmetric dense grid within $|b| < 15\deg$. The dense coverage of the bulge and inner Galaxy is for $l < 30 \deg$. Other special programs, like the Kepler-2 follow-up, have initial data in DR16. The circle sizes reflect the different field-of-view of APOGEE-N and APOGEE-S; see § \ref{['apogeeS']}.
• Figure 3: Spectroscopic Hertzsprung-Russell diagram, $T_{\rm eff}$ versus $\log~g$ for the main red star sample in APOGEE DR16. The points are color-coded by their total metal content, [M/H]. Dwarf-type stars, those with $\log~g$ > 3.7 dex, have calibrated stellar parameters for the first time in DR16. New stellar grids also provide reliable measurements to cooler temperatures than in previous DRs.
• Figure 4: The normalized surface density ($N(z)$) of the spectroscopically-confirmed objects used in the BOSS and eBOSS clustering programs. The SDSS-I,-II, and -III sample of confirmed quasars is also presented to demonstrate the gains in the number of quasars that eBOSS produced over the interval $0.8<z<2.2$.
• Figure 5: DR16 eBOSS spectroscopic coverage in Equatorial coordinates (map centered at RA = 8h.) Each symbol represents the location of a completed spectroscopic plate scaled to the approximate field of view. SPIDERS-maximal footprint is the same as BOSS, and SPIDERS-complete is SEQUELS. For more details on SPIDERS coverage see Comparat2020.