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Published August 2006 | Published
Journal Article Open

The Discovery of Three New z > 5 Quasars in the AGN and Galaxy Evolution Survey


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 midinfrared 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–3.7 µm). 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.

Additional Information

© 2006 The American Astronomical Society. Received 2006 March 12; accepted 2006 April 30. We greatly appreciate the help of Mark Dickinson and Steve Dawson with the Keck observations used here. R. J. C. is funded through a National Science Foundation Graduate Research Fellowship. X. F. acknowledges support from NSF grant AST 03-07384 and a Packard Fellowship for Science and Engineering. Both D. J. E. and X. F. receive support from an Alfred P. Sloan Research Fellowship. A. H. G. acknowledges support from an NSF Small Grant for Exploratory Research under award AST 04-36681. Observations reported here were obtained at the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona. This work made use of images and/or data products provided by the NOAO Deep Wide-Field Survey (Jannuzi & Dey 1999), which is supported by the National Optical Astronomy Observatory (NOAO). NOAO is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory (JPL), California Institute of Technology (Caltech), under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL Caltech. Some of the data presented here were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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