A survey of z > 5.7 quasars in the Sloan Digital Sky Survey. II - Discovery of three additional quasars at z > 6

We present the discovery of three new quasars at z > 6 in ∼ 1300 deg² of Sloan Digital Sky Survey imaging data, J114816.64+525150.3 (z = 6.43), J104845.05+463718.3 (z = 6.23), and J163033.90+401209.6 (z = 6.05). The first two objects have weak Lyα emission lines; their redshifts are determined from the positions of the Lyman break. They are only accurate to ∼0.05 and could be affected by the presence of broad absorption line systems. The last object has a Lyα strength more typical of lower redshift quasars. Based on a sample of six quasars at z > 5.7 that cover 2870 deg² presented in this paper and in Paper I, we estimate the comoving density of luminous quasars at z ∼ 6 and M₁₄₅₀ < -26.8 to be (8 ± 3) × 10^-10 Mpc^-3 (for H ₀ = 50 km s^-1 Mpc^-1, Ω = 1). Hubble Space Telescope imaging of two z > 5.7 quasars and high-resolution, ground-based images (seeing ∼0″.4) of three additional z > 5.7 quasars show that none of them is gravitationally lensed. The luminosity distribution of the high-redshift quasar sample suggests the bright-end slope of the quasar luminosity function at z ∼ 6 is shallower than ψ ∝ L^-3.5 (2 σ), consistent with the absence of strongly lensed objects.