The Sloan Digital Sky Survey Quasar Catalog: 12th Data Release


Following the tradition established by SDSS-I/II, the SDSS-III BOSS collaboration produces a quasar catalog.

The SDSS-DR12 (DR12Q) quasar catalog is the final SDSS-III quasar catalog. Its content is mostly based on the DR10Q one with new information on multiple spectroscopy and photometric variability.

The SDSS-DR12 Quasar catalog is fully described in Pâris et al. (2017) and we summarize below its main characteristics.

Note: This page describes the final SDSS-III Quasar Catalog. We recommend that you use the most recent version of the SDSS-IV Quasar Catalog, which is described on the Quasar Catalog page.

Catalog production


In order to detect the BAO scale in the Lyman-α forest at z~2.5, BOSS observed about 300,000 quasars with 184,000 of them being in the redshift range 2.15 < z < 4, where at least part of the Lyman-α forest lies in the SDSS spectral range. The target selection has been designed in order to provide at least 15 quasars with z > 2.15 per square degree. The catalog is therefore not uniform by construction but a uniform sample is also identified. Since BAO measurements require a catalog of maximal purity, all quasar candidates have been visually inspected.

Inspected quasar candidates

The objects that were inspected have been selected in three different ways:

Objects targeted as quasars by the main BOSS survey
The quasar target selection is described on the quasar target selection page and in detail in Ross et al. (2012).
Ancillary programs
Some BOSS ancillary programs target quasars through peculiar criteria (special selection, search for variability, peculiar AGN population etc...). Those objects have been included in the catalog, and extra flags indicate which ancillary program they are part of. The whole description of these flags can be found as part of the BOSS ancillary target documentation and in the BOSS overview and the DR11/DR12 papers. One of these ancillary programs is an SDSS-IV pilot survey, called SEQUELS, that have a series of dedicated target selection flags (EBOSS_TARGET0).
Serendipitous objects
Quasars might be targeted by chance by other programs, such as the luminous galaxy survey. In order to be as complete as possible, we also tried to identify serendipitous quasars. In particular, objects that the pipeline identified as QSO with z>2, or GALAXY/BROADLINE objects have been inspected.

Visual inspection

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? or QSO_BAL_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-DR12 Quasar Catalog only contains secure identifications (i.e. QSO and QSO_BAL). However, we also provide the full result of the visual inspection of the superset from which we derived DR12Q.

Catalog content

The full content of the SDSS-DR12 Quasar Catalog content can be found in Table 4 of Pâris et al. (2017) and the detailed description of the data model is available in the DR12Q documentation in the SDSS Data Model.

Description of the files

The SDSS-DR12 Quasar Catalog (DR12Q)

This file contains all the quasars of the SDSS-DR12 Quasar Catalog. 297,301 quasars have been identified. This sample is the one used by the SDSS-BOSS collaboration.

DR12Q.fits (513 MB): SDSS-DR12Q (Main catalog, fits format)

Detailed properties of BAL quasars

The primary quasar catalog provides global information on BAL quasars. We detail their trough-by-trough properties in this file. Its format is given in the associated data model.

DR12Q_BAL.fits (28 MB): Detailed properties of DR12Q BAL quasars (fits format)

Supplementary lists

We also provide two supplementary lists: a first one that contains quasars serendipitously discovered in the course of various tests to establish the visual inspection strategy, and a second one that contains quasars identified on plates that did not reach survey quality and were not re-observed later.
The format of the two supplementary lists is the same and is described here.

DR12Q_sup.fits (1.1 MB): Supplementary list that contains serendipitous quasars (fits format).

DR12Q_supbad.fits (92 kB): Supplementary list that contains quasars identified on bad plates (fits format).

DR12Q superset

All the quasar targets were visually inspected to derive DR12Q. This file contains the list of all the quasar targets together with the result of our visual inspection. The meaning of the visual inspection flags is given in Table 2 of Pâris et al. (2017) and the file format is detailed here.

Superset_DR12Q.fits (111 MB): Superset file from which DR12Q is derived (fits format)

Quasar spectra identified on bad plates

We release the list of quasars that were identified on bad plates. Individual spectra for those bad plates are not released so we provide them in this file.

spec_supbad.tar.gz (17 MB): Archive containing individual spectra of quasars identified on bad plates (fits format)