A Survey ofz > 5.7 Quasars in the Sloan Digital Sky Survey. III. Discovery of Five Additional Quasars

We present the discovery of five new quasars at z>5.7, selected from themulticolor imaging data of the Sloan Digital Sky Survey (SDSS). Three of them,at redshifts 5.93, 6.07, and 6.22, were selected from ~1700 deg^2 of new SDSSMain Survey imaging in the Northern Galactic Cap. An additional quasar, atredshift 5.85, was discovered by coadding the data obtained in the FallEquatorial Stripe in the SDSS Southern Survey Region. The fifth object, atredshift 5.80, is selected from a non-standard SDSS scan in the SouthernGalactic Cap outside the Main Survey area. The spectrum of SDSSJ162331.81+311200.5 (z=6.22) shows a complete Gunn-Peterson trough at z_abs >5.95, similar to the troughs detected in other three z>6.2 quasars known. Wepresent a composite spectrum of the z>5.7 quasars discovered in the SDSS todate. The average emission line and continuum properties of z~6 quasars exhibitno significant evolution compared to those at low redshift. Using a completesample of nine z>5.7 quasars, we find that the density of quasars with M_1450 <-26.7 at z~6 is (6+/-2) x 10^-10 per Mpc^3 consistent with our previousestimates. The luminosity distribution of the sample is fit with a power lawluminosity function Psi(L) ~ L^(-3.2+/-0.7), somewhat steeper than butconsistent with our previous estimates.Comment: AJ in press (Aug 2004), 18 pages, 4 figure