2000AJ....120.1167F

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 M₁₄₅₀=-27.2 (H₀=50 km.s^–1.Mpc^–1, q₀=0.5). The spectrum shows a strong and broad Lyα emission line, strong Lyα 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 IV emission lines similar to those of quasars at z≲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∼5.8. Using a high-resolution spectrum in the Lyα forest region, we place a conservative upper limit on the optical depth because of the Gunn-Peterson effect of τ<0.5 in regions of minimum absorption. The Lyα forest absorption in this object is much stronger than that in quasars at z≲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 ∼3x10⁹ 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 M₁₄₅₀←27 in a survey area of 600 deg² 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.