Evidence for a decrease in the space density of quasars at Z more than about 3.5

Results are reported for a survey made with a red-blazed grating prism and the CTIO 4 m telescope, and evidence is presented for the decrease of the apparent space density of quasars at redshifts greater than 3.5. Although no quasars with higher values that 3.5 have been found, enough quasars and emission-line objects of lower redshifts are discovered to provide a good estimate of the limiting sensitivity of the survey conducted. Because Lyman-alpha is normally the strongest line in quasar spectra, the fact that it is not seen in any of the survey objects while weaker ones are found is evidence of the scarcity of quasars with redshift values in the 3.7-4.7 range. The limit of the present survey is 1.2 mag fainter in emission-line flux than the limit of the Hoag-Smith (1977) survey.