The Sloan Digital Sky Survey Quasar Catalog: fourteenth data release
Following the tradition established by SDSS-I/II/III the SDSS-IV/eBOSS collaboration is producing a visually inspected quasar catalog. The SDSS-DR14 quasar catalog (DR14Q) is the first to be released that contains new identifications that are mostly from eBOSS. The DR14Q paper is in preparation, but the DR12 version (which contained final data from BOSS as well as data from the preliminary eBOSS survey SEQUELS) is detailed in Paris et al. (2017). Below, we summarize the main characteristics of DR14Q.
In order to provide the first direct measurement of the baryonic acoustic oscillations (BAO) scale at z ~ 1.5, eBOSS aims to uniformly select and successfully observe over 500,000 quasars in the redshift range 0.9 < z < 2.2, as well as recovering > 50,000 new quasars at z > 2.1 for Lyman-α forest measurements (see Myers et al. 2015 for details). Since clustering measurements require a catalog of maximal purity, quasar candidates suspected of having an incorrect pipeline redshift have been visually inspected. Note that DR14Q is not expected to be uniform, it is expected to be a more accurate census of quasars than using SDSS pipeline classifications and redshifts alone. The procedures necessary to obtain a uniform catalog for clustering studies are outlined in Section 3 of Ata et al. (2017).
Inspected quasar candidates
As the volume of SDSS-IV quasars is large compared to previous iterations of the SDSS, a new algorithm was applied for DR14Q in order to determine which quasars need to be visually inspected.
We start with the first five identifications produced by the SDSS spectroscopic pipeline (i.e. identifications corresponding to the five lowest values of reduced-χ2), the pipeline redshifts (zpipeline), and the ZWARNING quality flag. We then apply the following algorithm:
1. If the first SDSS pipeline identification is STAR, then the resulting classification is STAR;
2. If the first SDSS pipeline identification is GALAXY with zpipeline < 1, then the resulting classification is GALAXY;
3. If the first SDSS pipeline identification is GALAXY with zpipeline ≤ 1 and at least two other SDSS pipeline identifications are GALAXY, then the resulting classification is GALAXY;
4. If the first SDSS pipeline identification is QSO with ZWARNING = 0, then the resulting classification is QSO, except if at least two other SDSS pipeline identifications are STAR. In such a case, the resulting identification is STAR;
5. If the first pipeline identification is QSO with ZWARNING > 0 and at least two alternate SDSS pipeline identifications are STAR, then the resulting identification is STAR.
Each of these 5 criteria yield a classification (and redshift), which is retained as correct. If none of the 5 criteria is passed by an object, then the object is visually inspected. This approach results in ~7% of objects being visually inspected.
The visual inspection is performed to (i) secure the identification of the objects, (ii) reliably estimate the emission redshift of quasars, and (iii) identify peculiar features such as Damped Lyman-α systems (DLA) and Broad Absorption Lines (BAL). We therefore manually confirmed or modified the identification of the object and, when needed, corrected the redshift provided by the pipeline, i.e. when it was wrong (when e.g. an emission line is misidentified or a bad feature is considered an emission line) or inaccurate (when emission lines are correctly identified but not properly centered).
After visual inspection, each quasar candidate is classified among one of the following categories: QSO, QSO_BAL, QSO_Z? when we know this is a quasar but its redshift is not certain, QSO_? when the object is possibly a quasar, Star, Star_? when the object is possibly a star, Galaxy, ? when the identification is uncertain or Bad when the data are not good enough to ascertain identification. The SDSS-DR14 Quasar Catalog only contains secure identifications (i.e. QSO and QSO_BAL).
The DR14Q paper is in preparation, but the content of the SDSS-DR14 Quasar Catalog is similar to the description of DR12Q in Table 3 of Paris et al. (2017) and the detailed description of the data model is available here.
We are making the latest version of the DR14 quasar catalog (DR14Q_v3_1.fits) available. It should contain all of the quasars that comprise the SDSS-DR14 Quasar Catalog. Of order 526,000 quasars have so far been identified across the SDSS-I/II/III and IV surveys.
DR14Q_v3.1.fits (596 MB): SDSS-DR14Q visually inspected quasar catalog (fits format)
We warn users that although this catalog should be useful for identifying confirmed quasars in DR14, not all of the catalog fields have been fully populated yet. A final vetted version of the catalog should be available when the DR14 quasar catalog paper (Pâris et al., in preparation) is published.
Previously released SDSS quasar catalogs
We recommend that you use the DR14 quasar catalog for identifying confirmed quasars, as this catalog is the most recent one available. Previously released SDSS quasar catalogs are still available on the SAS, and are described in Pâris et al. (2017) for DR12, in Pâris et al. (2014) for DR10, and Pâris et al. (2012) for DR9. Corresponding data models for the quasar catalogs can be found here.