SIMBAD references

This paper presents the first results of a survey for bright quasars (V<14.5 and R<15.4) covering the northern hemisphere at Galactic latitudes |b|>30°. The photometric database is derived from the Guide Star and USNO catalogs. Quasars are identified on the basis of their X-ray emission measured in the ROSAT All-Sky Survey. The surface density of quasars brighter than 15.5 mag turns out to be (10±2)x10^–3 deg^–2, about 3 times higher than that estimated by the PG survey. The quasar optical luminosity function (LF) at 0.04<z≤0.3 is computed and shown to be consistent with a luminosity-dependent luminosity evolution of the type derived by La Franca & Cristiani in the range 0.3<z≤2.2. The predictions of semianalytical models of hierarchical structure formation agree remarkably well with the present observations.