Did Most High-Redshift Quasars Escape Detection?

Abstract

We present follow-up spectroscopy to the Calar Alto Deep Imaging Survey (CADIS), reporting on the quasars in the CADIS 16h-field, and including preliminary data from two other fields. In this 10' x 10' field we found six quasars at redshift z>2.2 which are brighter than R=22 mag, while surface densities determined in previous surveys are reported to be below one on average. This is the highest reported surface density of high-redshift quasars within the given limits. We believe this result to be a consequence of the multicolor database and the search technique used in CADIS. Our observations further seem to indicate that the density of high-redshift quasars is also higher than predicted by the luminosity function of Warren (1994) by a factor of three, implying that common search methods have overlooked the majority of high-redshift quasars at this magnitude level. In particular, an application of the V/V max test to our preliminary list of AGNs with R<22 mag and z<4 yields = 0.51 +-0.06, characterizing our preliminary redshift distribution as flat.