A survey of z∼6 quasars in the sloan digital sky survey deep stripe.: I.: A flux-limited sample at zAB<21

We present the discovery of five quasars at z similar to 6 selected from 260 deg(2) of the Sloan Digital Sky Survey (SDSS) southern survey, a deep imaging survey obtained by repeatedly scanning a stripe along the celestial equator. The five quasars with 20 < z(AB) < 21 are 1-2 magnitudes fainter than the luminous z similar to 6 quasars discovered in the SDSS main survey. One of them was independently discovered by the UKIRT Infrared Deep Sky Survey. These quasars, combined with another z similar to 6 quasar known in this region, make a complete flux-limited quasar sample at z(AB) < 21. The sample spans the redshift range 5.85 <= z <= 6.12 and the luminosity range -26.5 <= M-1450 <= -25.4 (H-0 = 70 km s(-1) Mpc(-1), Omega(m) = 0.3, and Omega(Lambda) = 0.7). We use the 1/V-a method to determine that the comoving quasar spatial density at < z > = 6.0 and < M-1450 > = -25.8 is (5.0 +/- 2.1) x 10(-9) Mpc(-3) mag(-1). We model the bright-end quasar luminosity function (QLF) at z similar to 6 as a power law Phi(L-1450) proportional to L-1450(beta). The slope beta calculated from a combination of our sample and the luminous SDSS quasar sample is -3.1 +/- 0.4, significantly steeper than the slope of the QLF at z similar to 4. Based on the derived QLF, we find that the quasar/active galactic nucleus (AGN) population cannot provide enough photons to ionize the intergalactic medium (IGM) at z similar to 6 unless the IGM is very homogeneous and the luminosity (L-1450(*)) at which the QLF power law breaks is very low.