The Discovery of Five Quasars at z>4 Using the Second Palomar Sky Survey

Abstract

We are conducting a survey to identity z > 4 quasars using a digital version of the Second Palomar Sky Survey. The plates are taken in the photographic JFN bands and calibrated to the Gunn-Thuan gri system, making these data suitable for a multicolor search for quasars in the redshift range of 4.0 <~ z <~ 4.8. A new software package, SKICAT, was developed to perform automatic reduction of these scans into object catalogs, to classify the objects as stars or galaxies to faint levels objectively using a machine learning decision tree method, and to allow for easy manipulation of the final catalogs. Here we report on the initial results from this survey. We have selected high-redshift quasar candidates from 14 fields with a total area covered of ~560 deg^2^ over the magnitude range 16.5 <= m_r_ <= 19.6. Follow-up work is now well underway, and is complete for several fields. Here we present a preliminary description of the survey as well a spectroscopy, coordinates, and finding charts for our first five z > 4 quasars.