The DR16 quasar value added catalog provides spectroscopic and photometric data for over 750,000 known quasars from all four SDSS observation campaigns (SDSS-I/II/III/IV). SDSS quasar catalogs have a long history of visually inspecting quasar spectra for improved classifications, redshifts, and features of interest. These catalogs are broadly useful to the community, but also have general utility by finding archetypical and problematic objects to help test automated spectroscopic reduction and classification pipelines. In that vein, DR16Q is the largest and final quasar catalog from SDSS-IV/eBOSS, and comprises both a "superset" of more than 1.44 million quasar-targeted spectroscopic observations (DR16Q_Superset_v3), and a quasar-only catalog (DR16Q_v4) with more than 920,000 observations of 750,000 quasars. The quasar-only catalog includes multi-wavelength photometric data cross-matched from the following external surveys: GALEX, UKIDSS, WISE, FIRST, 2MASS, ROSAT/2RXS, XMM-Newton, and Gaia.
DR16Q provides the largest number of redshift estimates, per quasar, for an SDSS quasar VAC, including redshifts from previous catalogs (DR7Q, DR12Q), two sets of "Hewett and Wild" improved redshifts (DR6; Hewett and Wild 2010, DR7Q; Shen et al. 2011), automated eBOSS pipeline redshifts, visual inspection redshifts, PCA-derived redshifts, and six emission line redshifts for Hα, Hβ, Mg II, C III], C IV, and Lyα. Information on damped Lyman alpha (DLA) and broad absorption line (BAL) quasars was included from automated algorithms for 35,686 DLAs and 99,856 BALs. BAL flags from previous catalogs have also been retained.
The catalog is described in Lyke et al. (2020) and also on the website listed above.
Older versions of this VAC based on previous data releases are still available, and linked on the website above. We always recommend that you use the latest version of this VAC. A list of known bugs (and their fixes in DR16Q) appearing in previous catalogs can be found in Appendix C of Lyke et al. (2020).