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

We present the discovery of three z>5 quasars in the AGN and Galaxy EvolutionSurvey (AGES) spectroscopic observations of the NOAO Deep Wide-Field Survey(NDWFS) Bootes Field. These quasars were selected as part of a larger Spitzermid-infrared quasar sample with no selection based on optical colors. Thehighest redshift object, NDWFS J142516.3+325409, z=5.85, is thelowest-luminosity z>5.8 quasar currently known. We compare mid-infraredtechniques for identifying z>5 quasars to more traditional optical techniquesand show that mid-infrared colors allow for selection of high-redshift quasarseven at redshifts where quasars lie near the optical stellar locus and at z>7where optical selection is impossible. Using the superb multi-wavelengthcoverage available in the NDWFS Bootes field, we construct the spectral energydistributions (SEDs) of high-redshift quasars from observed Bw-band to 24microns (rest-frame 600 Angstroms - 3.7 microns). We show that the threehigh-redshift quasars have quite similar SEDs, and the rest-frame composite SEDof low-redshift quasars from the literature shows little evolution compared toour high-redshift objects. We compare the number of z>5 quasars we havediscovered to the expected number from published quasar luminosity functions.While analyses of the quasar luminosity function are tenuous based on onlythree objects, we find that a relatively steep luminosity function with PsiL^(-3.2) provides the best agreement with the number of high-redshift quasarsdiscovered in our survey.Comment: 9 page, 7 figures. Accepted for publication in A