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We present the discovery of three new quasars at z>6 in 1300 deg² of SDSS 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 Ly alpha 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 Ly alpha 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 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-redshfit quasar sample suggests the bright end slope of the quasar luminosity function at z 6 is shallower than Psi L^-3. 5 (2-sigma), consistent with the absence of strongly lensed objects.
Fan et al. (Tue,) studied this question.