SDSSQSOCand. ivo://nasa.heasarc/sdssnbcqsc NASA/GSFC HEASARC Richards et al. 2026-04-03 NASA/GSFC HEASARC help desk heasarc-vo at athena.gsfc.nasa.gov AGN The Nonparametric Bayes Classifier (NBC) Quasar Candidate Catalog is a catalog of 100,563 unresolved, UV-excess (UVX) quasar candidates with magnitudes to as faint as 21 in the g-band from 2099 square degrees of the Sloan Digital Sky Survey (SDSS) Data Release One (DR1) imaging data. Existing spectra of 22,737 sources reveals that 22,191 (97.6%) are quasars; accounting for the magnitude dependence of this efficiency, the authors estimate that 95,502 (95.0%) of the objects in the catalog are quasars. Such a high efficiency is unprecedented in broadband surveys of quasars. This "proof-of-concept" sample is designed to be maximally efficient, but still has 94.7% completeness to unresolved, g ~< 19.5, UVX quasars from the DR1 quasar catalog. This efficient and complete selection is the result of the application of a probability density type analysis to training sets that describe the four-dimensional color distribution of stars and spectroscopically confirmed quasars in the SDSS. Specifically, the authors use a nonparametric Bayesian classification, based on kernel density estimation, to parametrize the color distribution of astronomical sources - allowing for fast and robust classification. They further supplement the catalog by providing photometric redshifts and matches to FIRST/VLA, ROSAT, and USNO-B sources. Much more information on the SDSS is available at the project's web site at <a href="http://www.sdss.org/">http://www.sdss.org/</a>. This database table was created by the HEASARC in August 2005 based on CDS table J/ApJS/155/257/table1.dat. This is a service provided by NASA HEASARC . 2004ApJS..155..257R https://heasarc.gsfc.nasa.gov/W3Browse/all/sdssnbcqsc.html Catalog Research served-by HEASARC TAP https://heasarc.gsfc.nasa.gov/xamin/vo/cone?showoffsets&table=sdssnbcqsc& GET text/xml 180 99999 true 4.3401891 -11.2568801 0.0166666666666667 https://heasarc.gsfc.nasa.gov/xamin/vo/tap https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=sdssnbcqsc GET text/xml https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3query.pl?tablehead=name=heasarc_sdssnbcqsc&Action=More+Options&Action=Parameter+Search&ConeAdd=1 GALAXY CATALOG 0.0166666666666667 Optical public sdssnbcqsc Sloan Digital Sky Survey NBC Quasar Candidate Catalog rmag_error Error in rmag mag stat.error;phot.mag;em.opt.R double nullable row_pixel Row Position of Object in Field pixel pos.cartesian.x;instr.det double nullable "__x_ra_dec" System unit vector column double nullable sdss_name SDSS Designation meta.id char nullable ra Right Ascension degree pos.eq.ra;meta.main double nullable bii Galactic Latitude degree pos.galactic.lat double nullable imag_error Error in imag mag stat.error;phot.mag;em.opt.I double nullable redshift_probability Photometric Redshift Range Probability stat.likelihood;src.redshift.phot double nullable redshift_lower_limit Lower Limit in Redshift stat.error;src.redshift.phot double nullable rmag_extinction Galactic Extinction in the r Band mag phys.absorption;em.opt.R double nullable rmag PSF r asinh Magnitude mag phot.mag;em.opt.R double nullable dec Declination degree pos.eq.dec;meta.main double nullable previous_redshift Previous Catalog Object Redshift src.redshift double nullable zmag_error Error in zmag mag stat.error;phot.mag;em.opt double nullable imag_extinction Galactic Extinction in the i Band mag phys.absorption;em.opt.I double nullable rass_count_rate RASS Full-Band Count Rate ct/s phot.count;em.X-ray.soft double nullable gmag_extinction Galactic Extinction in the g Band mag phys.absorption;em.opt double nullable "__y_ra_dec" System unit vector column double nullable redshift_upper_limit Upper Limit in Redshift stat.error;src.redshift.phot double nullable gmag PSF g asinh Magnitude mag phot.mag;em.opt double nullable proper_motion Proper Motion (mas/yr) mas/yr pos.pm double nullable lii Galactic Longitude degree pos.galactic.lon double nullable sdss_id SDSS Object Identifier meta.id char nullable imag PSF i asinh Magnitude mag phot.mag;em.opt.I double nullable gmag_error Error in gmag mag stat.error;phot.mag;em.opt double nullable zmag PSF z asinh Magnitude mag phot.mag;em.opt double nullable zmag_extinction Galactic Extinction in the z Band mag phys.absorption;em.opt double nullable umag PSF u asinh Magnitude mag phot.mag;em.opt.U double nullable umag_extinction Galactic Extinction in the u Band mag phys.absorption;em.opt.V double nullable umag_error Error in umag mag stat.error;phot.mag;em.opt.U double nullable redshift Photometric Redshift src.redshift.phot double nullable "__z_ra_dec" System unit vector column double nullable "__row" System index column char nullable quasar_density KDE Quasar Probability Density double nullable column_pixel Column Position of Object in Field pixel pos.cartesian.y;instr.det double nullable previous_class Previous Catalog Object Classification src.class char nullable flux_20_cm 20-cm Flux Density (mJy) mJy phot.flux.density;em.radio.750-1500MHz double nullable name Catalog Designation meta.id;meta.main char nullable star_density KDE Star Probability Density double nullable