Efficient photometric selection of quasars from the sloan digital sky survey. II. ∼1,000,000 quasars from data release 6

Gordon T. Richards, Adam D. Myers, Alexander G. Gray, Ryan N. Riegel, Robert C. Nichol, Robert J. Brunner, Alexander S. Szalay, Donald P. Schneider, Scott F. Anderson

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Abstract

We present a catalog of 1,172,157 quasar candidates selected from the photometric imaging data of the Sloan Digital Sky Survey (SDSS). The objects are all point sources to a limiting magnitude of i = 21.3 from 8417 deg2 of imaging from SDSS Data Release 6 (DR6). This sample extends our previous catalog 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 our previous sample and ∼10 times the size of the largest spectroscopic quasar catalog. Cross-matching between our 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, we provide photometric redshift estimates (typically good to Δz ± 0.3 [2σ]) and cross-matching with radio, X-ray, and proper-motion catalogs. Finally, we consider 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.

Original languageEnglish (US)
Pages (from-to)67-83
Number of pages17
JournalAstrophysical Journal, Supplement Series
Volume180
Issue number1
DOIs
StatePublished - Sep 7 2009

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Richards, G. T., Myers, A. D., Gray, A. G., Riegel, R. N., Nichol, R. C., Brunner, R. J., Szalay, A. S., Schneider, D. P., & Anderson, S. F. (2009). Efficient photometric selection of quasars from the sloan digital sky survey. II. ∼1,000,000 quasars from data release 6. Astrophysical Journal, Supplement Series, 180(1), 67-83. https://doi.org/10.1088/0067-0049/180/1/67