The discovery of three new z > 5 quasars in the AGN and Galaxy Evolution Survey

Richard J. Cool, Christopher S. Kochanek, Daniel J. Eisenstein, Daniel Stern, Kate Brand, Michael J.I. Brown, D. E.Y. Arjun, Peter R. Eisenhardt, F. A.N. Xiaohui, Anthony H. Gonzalez, Richard F. Green, Buell T. Jannuzi, Eric H. Mckenzie, George H. Rieke, Marcia Rieke, Baruch T. Soifer, Hyron Spinrad, Richard J. Elston

Research output: Contribution to journalArticlepeer-review

54 Scopus citations


We present the discovery of three z > 5 quasars in the AGN and Galaxy Evolution Survey spectroscopic observations of the NOAO Deep Wide-Field Survey (NDWFS) Bootes Field. These quasars were selected as part of a larger Spitzer mid-infrared quasar sample, with no selection based on optical colors. The highest redshift object, NDWFS J142516.3+325409, at z = 5.85, is the lowest luminosity z > 5.8 quasar currently known. We compare mid-infrared techniques for identifying z > 5 quasars to more traditional optical techniques and show that mid-infrared colors allow for the selection of high-redshift quasars even at redshifts at which quasars lie near the optical stellar locus and at z > 7, where optical selection is impossible. Using the superb multiwavelength coverage available in the NDWFS Bootes field, we construct the spectral energy distributions (SEDs) of high-redshift quasars from observed B w band to 24 μm (rest-frame 600 Å-3.7μm). We show that the three high-redshift quasars have quite similar SEDs, and the rest-frame composite SED of low-redshift quasars from the literature shows little evolution compared to our high-redshift objects. We compare the number of z > 5 quasars we have discovered to the expected number from published quasar luminosity functions. While analyses of the quasar luminosity function are tenuous based on only three objects, we find that a relatively steep luminosity function with ψ ∝ L -3.2 provides the best agreement with the number of high-redshift quasars discovered in our survey.

Original languageEnglish (US)
Pages (from-to)823-830
Number of pages8
JournalAstronomical Journal
Issue number2
StatePublished - Aug 2006


  • Quasars: emission lines
  • Quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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