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A. Constantin, J. C. Shields (Ohio U.), F. Hamann (Univ. Florida)
A growing number of QSOs are now known to exist at redshifts beyond 4, and these sources provide important opportunities for better understanding of the astrophysics of galaxy formation and evolution. To date there are ~130 known QSOs with z > 4, but only limited efforts have been made to survey systematically the emission-line properties of these objects and/or the selection effects related with the techniques by which they were discovered. In this poster we will present results of a program of high signal-to-noise spectroscopy for 44 QSOs using the MMT and Keck observatories. The majority of these sources were originally identified via color selection techiques. The quasar spectra cover wavelengths between 1100 Å\ and 1700 Å\ in the rest frame, for sources spanning a luminosity range of ~ 2 orders of magnitude. An examination of the luminosity dependence of the emission features reveals evidence for a weak Baldwin effect. Spectrum composites for the whole data set and for subsets are obtained and analysed in order to investigate the spectral dependence on selection effects. The results show a tendency for stronger C~IV emission lines for color-selected quasars, than for grism-selected objects.