The discovery of a luminous z=5.80 quasar from the Sloan Digital Sky Survey

We present observations of SDSSp J104433.04-012502.2, a luminous quasar at z = 5.80 discovered from Sloan Digital Sky Survey (SDSS) multicolor imaging data. This object was selected as an i'-band dropout object, with i* = 21.8 +/- 0.2 and z* = 19.2 +/- 0.1. It has an absolute magnitude M(1450) = -27.2 (H(0) = 50 km s(-1) Mpc(-1), q(0) = 0.5). The spectrum shows a strong and broad Ly alpha emission line, strong Ly alpha forest absorption lines with a mean continuum decrement D(A) = 0.91 and a Lyman limit system at z = 5.72. The spectrum also shows strong O I and Si rv emission lines similar to those of quasars at z less than or similar to 5, suggesting that these metals were produced at a redshift beyond 6. The lack of a Gunn-Peterson trough in the spectrum indicates that the universe is already highly ionized at z similar to 5.8. Using a high-resolution spectrum in the Ly alpha forest region, we place a conservative upper limit on the optical depth because of the Gunn-Peterson effect of tau < 0.5 in regions of minimum absorption. The Ly alpha forest absorption in this object is much stronger than that in quasars at z less than or similar to 5. The object is unresolved in a deep image with excellent seeing, implying that it is unlensed. The black hole mass of this quasar is similar to 3 x 10(9) M. if we assume no lensing amplification and that it is radiating at the Eddington luminosity, implying that it resides in a very massive dark matter halo. The discovery of one quasar at M(1450) < -27 in a survey area of 600 deg(2) is consistent with an extrapolation of the observed luminosity function at lower redshifts. The abundance and evolution of such quasars can provide sensitive tests for models of quasar and galaxy formation.