SDSSNBCKDE ivo://nasa.heasarc/sdssnbckde NASA/GSFC HEASARC Richards et al. 2026-10-09 NASA/GSFC HEASARC help desk heasarc-vo at athena.gsfc.nasa.gov Survey Source This table contains a catalog of 1,015,082 quasar candidates selected from the photometric imaging data of the Sloan Digital Sky Survey (SDSS) using a non-parametric Bayesian classification kernel density estimator (NBC-KDE). It excludes 157,075 initial candidates that were culled as known or likely contaminants. The objects are all point sources to a limiting magnitude of i = 21.3 from 8417 deg&lt;sup&gt;2&lt;/sup&gt; of imaging from SDSS Data Release 6 (DR6). This sample extends the previous catalog (Paper I: Richards et al. 2004, ApJS, 155, 257) by using the latest SDSS public release data and probing both ultraviolet (UV)-excess and high-redshift quasars. While the addition of high-redshift candidates reduces the overall efficiency (quasars:quasar candidates) of the catalog to ~80%, it is expected to contain no fewer than 850,000 bona fide quasars, which is ~8 times the number of the previous sample and ~10 times the size of the largest spectroscopic quasar catalog. Cross-matching between this photometric catalog and spectroscopic quasar catalogs from both the SDSS and 2dF survey yields 88,879 spectroscopically confirmed quasars. For judicious selection of the most robust UV-excess sources (~500,000 objects in all), the efficiency is nearly 97 - more than sufficient for detailed statistical analyses. The catalog&#39;s completeness to type 1 (broad-line) quasars is expected to be no worse than 70%, with most missing objects occurring at z &lt; 0.7 and 2.5 &lt; z &lt; 3.0. In addition to classification information, the authors provide photometric redshift estimates (typically good to Delta(z) +/- 0.3 [2-sigma]) and cross-matching with radio, X-ray, and proper-motion catalogs. Finally, the authors have considered the catalog&#39;s utility for determining the optical luminosity function of quasars and are able to confirm the flattening of the bright-end slope of the quasar luminosity function at z ~ 4 as compared to z ~ 2. Much more information on the SDSS is available at the project&#39;s web site at &lt;a href="http://www.sdss.org/"&gt;http://www.sdss.org/&lt;/a&gt;. This table was created by the HEASARC based on an electronic version of Table 1 in the reference paper which was obtained from the ApJ web site. This is a service provided by NASA HEASARC . 2009ApJS..180...67R https://heasarc.gsfc.nasa.gov/W3Browse/all/sdssnbckde.html Catalog Research served-by HEASARC TAP https://heasarc.gsfc.nasa.gov/xamin/vo/cone?showoffsets&table=sdssnbckde& GET text/xml 180 99999 true 4.3401858 -11.2568751 0.0166666666666667 https://heasarc.gsfc.nasa.gov/xamin/vo/tap https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=sdssnbckde GET text/xml https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3query.pl?tablehead=name=heasarc_sdssnbckde&Action=More+Options&Action=Parameter+Search&ConeAdd=1 GALAXY CATALOG 0.0166666666666667 Optical public sdssnbckde SDSS NBCKDE Catalog of Photometrically Selected Quasar Candidate name SDSS Source Designation (SDSS Jhhmmss.ss+-ddmmss.s) meta.id;meta.main char nullable ra Right Ascension degree pos.eq.ra;meta.main double nullable dec Declination degree pos.eq.dec;meta.main double nullable rmag r-band PSF-ubercalibrated asinh Magnitude mag phot.mag;em.opt.R double nullable rmag_error Error in rmag mag stat.error;phot.mag;em.opt.R double nullable redshift Photometric Redshift; See Weinstein et al. 2004 src.redshift double nullable previous_redshift Previous Catalog Object Redshift src.redshift double nullable "__x_ra_dec" System unit vector column double nullable "__y_ra_dec" System unit vector column double nullable "__z_ra_dec" System unit vector column double nullable "__row" System index column char nullable reddening The (B-V) Extinction mag phot.color.excess double nullable redshift_probability Photometric Redshift Range Probability stat.probability;src.redshift double nullable uvxts_flag UV-Excess Flag, 88% Star Prior; See Paper I meta.code short nullable proper_motion Proper Motion (mas/yr) mas/yr pos.pm double nullable previous_classification Previous Catalog Object Classification meta.code.class;src.class char nullable log_star_density Logarithm of KDE Star Density meta.code;stat.probability double nullable lowzts_flag Low z Range Flag (z <= 2.2), 98% Star Prior meta.code short nullable redshift_upper_limit Upper Limit of Photometric Redshift src.redshift;stat.max double nullable zmag z-band PSF-ubercalibrated asinh Magnitude mag phot.mag;em.opt.I double nullable moving_flag Flag Indicates Possible Moving Object meta.code short nullable lii Galactic Longitude degree pos.galactic.lon double nullable gmag_error Error in gmag mag stat.error;phot.mag;em.opt.B double nullable zmag_error Error in zmag mag stat.error;phot.mag;em.opt.I double nullable redshift_lower_limit Lower Limit of Photometric Redshift src.redshift;stat.min double nullable imag_error Error in imag mag stat.error;phot.mag;em.opt.R double nullable bii Galactic Latitude degree pos.galactic.lat double nullable concentration Concentration for Star/Galaxy Separation meta.code double nullable qsots_flag Full z Range Flag, 95% Star Prior meta.code short nullable imag i-band PSF-ubercalibrated asinh Magnitude mag phot.mag;em.opt.R double nullable quality_flag Flag Indicates Quality: 6=Most Robust, -6=Least meta.code.qual short nullable source_number Sequential Identification Number for Each Source in Catalog meta.id;src int nullable highzts_flag High z Range Flag (z >= 3.5), 98% Star Prior meta.code short nullable flux_20_cm 20-cm Flux Density (mJy) mJy phot.flux.density;em.radio.750-1500MHz double nullable umag u-band PSF-ubercalibrated asinh Magnitude mag phot.mag;em.opt.U double nullable log_quasar_density Logarithm of KDE Quasar Density meta.code;stat.probability double nullable midzts_flag Mid z Range Flag (2.2 < z < 3.5), 98% Star Prior meta.code short nullable sdss_object_id SDSS Object Identification meta.id char nullable gmag g-band PSF-ubercalibrated asinh Magnitude mag phot.mag;em.opt.B double nullable umag_error Error in umag mag stat.error;phot.mag;em.opt.U double nullable rass_count_rate RASS Full-Band Count Rate (ct/s) ct/s phot.count;em.X-ray.soft double nullable