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Description
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<sup>2</sup> 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's completeness to type 1 (broad-line) quasars is expected to be no worse than 70%, with most missing objects occurring at z < 0.7 and 2.5 < z < 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'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's web site at <a href="http://www.sdss.org/">http://www.sdss.org/</a>. 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 .
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