SIMBAD references

We report the first results of an observational programme designed to determine the luminosity density of high-redshift quasars (z > 5 quasars) using deep multicolour CCD data. We report the discovery and spectra of three i < 21.5 high-redshift (z > 4.4) quasars, including one with (z > 5). At z = 5.17, this is the fourth highest redshift quasar currently published. Using these preliminary results we derive an estimate of the M_B < -25.0 (M_AB1450 < -24.5) quasar space density in the redshift range 4.8 < z < 5.8 of 3.6 ± 2.5 10^–8 Mpc^–3. When completed, the survey will provide a firm constraint on the contribution to the ionizing UV background in the redshift range 4.5 - 5.5 from quasars by determining the faint-end slope of the quasar luminosity function. The survey uses imaging data taken with the 2.5-m Isaac Newton Telescope as part of the Public Isaac Newton Group Wide Field Survey (WFS). This initial sample of objects is taken from two fields of effective area ∼12.5deg² from the final ∼100deg².