Photometric redshifts of quasars

Gordon T. Richards, Michael A. Weinstein, Donald P. Schneider, Xiaohui Fan, Michael A. Strauss, Daniel E. Vanden Berk, James Annis, Scott Burles, Emily M. Laubacher, Donald G. York, Joshua A. Frieman, David Johnston, Ryan Scranton, James E. Gunn, Željko Ivezić, R. C. Nichol, Tamás Budavári, István Csabai, Alexander S. Szalay, Andrew J. ConnollyGyula P. Szokoly, Neta A. Bahcall, Narciso Benítez, J. Brinkmann, Robert Brunner, Masataka Fukugita, Patrick B. Hall, G. S. Hennessy, G. R. Knapp, Peter Z. Kunszt, D. Q. Lamb, Jeffrey A. Munn, Heidi J.O. Newberg, Chris Stoughton

Research output: Contribution to journalArticlepeer-review

90 Scopus citations


We demonstrate that the design of the Sloan Digital Sky Survey (SDSS) filter system and the quality of the SDSS imaging data are sufficient for determining accurate and precise photometric redshifts of quasars. Using a sample of 2625 quasars, we show that "photo-z" determination is even possible for z ≤ 2.2 despite the lack of a strong continuum break, which robust photo-z techniques normally require. We find that, using our empirical method on our sample of objects known to be quasars, approximately 70% of the photometric redshifts are correct to within Δz = 0.2; the fraction of correct photometric redshifts is even better for z > 3. The accuracy of quasar photometric redshifts does not appear to be dependent upon magnitude to nearly 21st magnitude in i′. Careful calibration of the color-redshift relation to 21st magnitude may allow for the discovery of ∼106 quasar candidates in addition to the 105 quasars that the SDSS will confirm spectroscopically. We discuss the efficient selection of quasar candidates from imaging data for use with the photometric redshift technique and the potential scientific uses of a large sample of quasar candidates with photometric redshifts.

Original languageEnglish (US)
Pages (from-to)1151-1162
Number of pages12
JournalAstronomical Journal
Issue number3
StatePublished - Sep 2001

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Galaxies: distances and redshifts
  • Galaxies: photometry
  • Methods: statistical
  • Quasars: general


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