z ∼ 6 quasars from the Sloan Digital Sky Survey

We present the recent results on a survey for quasars at z similar to 6, selected from similar to 3000 deg(2) of multicolor imaging data from the Sloan Digital Sky Survey (SDSS). Seven luminous (M similar to -27) quasars at 5.7 < z < 6.4 are discovered. The existence of strong metal lines in the quasar spectra suggests early metal enrichment in the quasar environment. These quasars, if not gravitationally lensed, are located in supermassive black holes of M similar to 10(9-10) M-circle dot, indicating rapid formation of supermassive black hole population in the early universe, probably coeval with the formation of the first generation galaxies. A number of z similar to 6 quasars show strong dust and gas emission in sub-millimeter and radio wavelengths, further indicating close ties to the early star-formation activity in their host galaxies. We find that at z = 6, the comoving density of luminous quasars declines by a factor of similar to 20 from z similar to 3. The observations of quasar luminosity function will put strong constraint on the models of black hole evolution.