SDSS NBCKDE Catalog: 1 Million Photometrically Selected Quasar Candidates

Sloan Digital Sky Survey (SDSS) Data Release 6 imaging data covering 8417 square degrees was used to create a catalog of 1,015,082 quasar candidates. The catalog, produced by NASA HEASARC, extends a previous sample by probing both UV-excess and high-redshift quasars and is expected to contain at least 850,000 bona fide quasars. It includes photometric redshift estimates and cross-matching with radio, X-ray, and proper-motion catalogs.

Use Cases

• Training photometric classification models based on the non-parametric Bayesian classification kernel density estimator (NBC-KDE) method described.
• Studying the quasar luminosity function, particularly the flattening of the bright-end slope at high redshift mentioned in the description.
• Cross-matching candidate lists with spectroscopic confirmations or other multi-wavelength catalogs (radio, X-ray) as referenced.
• Analyzing the completeness and efficiency of photometric selection for type 1 quasars across different redshift ranges.

Strengths

• Large scale with 1,015,082 candidates, expected to contain at least 850,000 bona fide quasars.
• Includes 88,879 spectroscopically confirmed quasars from cross-matching with SDSS and 2dF surveys.
• Provides photometric redshift estimates with typical accuracy of Delta(z) +/- 0.3 (2-sigma).
• For a subset of ~500,000 robust UV-excess sources, the catalog efficiency is nearly 97%.

Limitations

• Column-level documentation is absent; field semantics must be inferred after download.
• Overall catalog efficiency for quasar candidates is reduced to ~80% due to the inclusion of high-redshift candidates.
• Completeness for type 1 quasars is no worse than 70%, with most missing objects in specific redshift ranges (z < 0.7 and 2.5 < z < 3.0).

Provenance

Source

NASA HEASARC, based on Table 1 from the reference paper (Richards et al. 2009).

Collection Method

Photometric selection from SDSS DR6 imaging using a non-parametric Bayesian classification kernel density estimator (NBC-KDE).

Time Range

Based on SDSS Data Release 6 (DR6).

Freshness

Last updated 2026-03-13 17:56:05.044114; freshness should be verified.

Geography

Sky coverage from 8417 deg² of SDSS imaging.