A study of ten quasars with redshifts greater than four

In this paper we report the discovery of four quasars with redshifts in excess of four. The objects were initially detected in a low-resolution CCD grism survey. All four have strong Lyα emission lines and have brightnesses of r~20. These observations raise the number of known z>4 quasars to ten. We present CCD photometry and high signal-to-noise, moderate-resolution (25 A) spectra of all ten quasars. Nine of the objects have -27.5 < M_B_ < -25; the tenth quasar has M_B_ = -29. The spectra of these ten quasars are similar, in terms of the emission lines and shapes of the continua, to the spectra of lower-redshift quasars. There is some marginal evidence that the C IV emission lines are weaker than those found in lower-redshift quasars. The continua redward of Lyα have spectral energy indices (fnu_ is proportional to valpha^ ranging from -1.39 to -0.35; the average value of α is -0.82 +/- 0.09. The continua of all of the quasars show strong (~1 mag) depressions blueward of the Lyα emission line; this is roughly twice the value seen in quasars at a redshift of three. Spectra of three of the ten quasars possess deep (zero flux in the center of the line at this resolution) absorption features blueward of Lyα.