Received ; accepted – 2 – ABSTRACT Very deep imaging data of three optically luminous radio-loud quasars with redshifts between z = 0.9 and z = 1.36 are presented. The data are complete for galaxies down to R = 26. There is no evidence for excess numbers of galaxies around the quasars; foreground galaxy clusters are excluded by the data as well as clusters with richness classes greater than 1 a...

We have selected quasars with X-ray colors suggestive of a low energy cutoff, from the ROSAT PSPC pointed archive. We examine the radio and optical properties of these 13 quasars. Five out of the seven quasars with good optical spectra show associated optical absorption lines, with two having high ∆v candidate systems. Two other cut-off quasars show reddening associated with the quasar. We conc...

The lifetime of the luminous phase of quasars is constrained by current observations to be 10 ∼< tQ ∼< 10 years, but is otherwise unkown. We model the quasar luminosity function in detail in the optical and X–ray bands using the Press–Schechter formalism, and show that the expected clustering of quasars depends strongly on their assumed lifetime tQ. We quantify this dependence, and find that ex...

Quasars at z > 4 provide direct information on the first massive structures to form in the Universe. Recent ground-based optical surveys (e.g., the Sloan Digital Sky Survey) have discovered large numbers of high-redshift quasars, increasing the number of known quasars at z > 4 to ≈ 500. Most of these quasars are suitable for follow-up X-ray studies. Here we review X-ray studies of the highest r...

In the two parts of this contribution we describe two related XMM-Newton programs. The first part summarizes our study of the X-ray spectral properties and variability of z>4 quasars (Shemmer et al. 2005). The second part presents preliminary results from our ongoing XMM-Newton program to investigate the X-ray spectral properties and variability of luminous, high accretion-rate quasars at z∼2–3...

We present spectroscopic observations of a sample of faint Gigahertz Peaked Spectrum (GPS) radio sources drawn from the Westerbork Northern Sky Survey (WENSS). Redshifts have been determined for 19 (40%) of the objects. The optical spectra of the GPS sources identified with low redshift galaxies show deep stellar absorption features. This confirms previous suggestions that their optical light i...

The Canada-France High-z Quasar Survey (CFHQS) is an optical survey designed to locate quasars during the epoch of reionization. In this paper we present the discovery of the first four CFHQS quasars at redshift greater than 6, including the most distant known quasar, CFHQS J2329-0301 at z = 6.43. We describe the observational method used to identify the quasars and present optical, infrared, a...

We link the lack of FR I type structure among quasars to the void of radio loud quasars below a critical disk luminosity of 10 46 erg/sec in the PG sample. We argue that the opening angle of the obscuring torus in radio loud quasars depends on the power of the central engine, approaching the jet's beaming angle near the FRI/FR II break. Consequently, low power radio quasars would either be clas...

We present the clustering of DEEP2 galaxies at 0.7 < z < 1.4 around quasars identified using both the SDSS and DEEP2 surveys. We measure the two-point cross-correlation of a sample of 36 opticallyselected, spectroscopically-identified quasars from the SDSS and 16 more found in the DEEP2 survey with the full DEEP2 galaxy sample over scales 0.1 < rp < 10 h −1 Mpc. The clustering amplitude is foun...

We apply a simple statistical method (Derenzo & Hildebrand 1969) to estimating the completeness of quasar surveys. It requires that an area has been covered by two or more, preferably different, selection techniques. We use three suitable data sets with separate selections from: variability and UV-excess (170 quasars); objective prism and UV-excess (141 quasars); multicolour and X-ray (ROSAT, 1...