Semi-analytic models of galaxy formation postulate the existence of virialized gaseous halos around galaxies at high redshifts. A small fraction of the light emitted by any high-redshift quasar is therefore expected to scatter off the free electrons in the halo of its host galaxy. The broadening of the scattered emission lines of the quasar can be used to measure the temperature of these electr...

We report the discovery of an unambiguous, substantial low-energy cutoff in the broad band X-ray spectrum of the radio quasar RX J1028.6-0844 at a redshift of 4.276 obtained with the ASCA satellite, which we preferably explained as indication of excess X-ray absorption. The equivalent hydrogen column density of the absorbing matter, depending on the redshift and metallicity, ranges from 2.5 102...

A number of deep, wide-field, near-infrared surveys employing new infrared cameras on 4m-class telescopes are about to commence. These surveys have the potential to determine the fraction of luminous dust-obscured quasars that may have eluded surveys undertaken at optical wavelengths. In order to understand the new observations it is essential to make accurate predictions of surface densities a...

We present photometric and spectroscopic observations of two close quasar– quasar pairs found in the Large Bright Quasar Survey (LBQS) (Hewett et al. 1995, AJ, 109, 1498). The two components of the 2153-2056 pair (z = 1.845, ∆θ = 7. 8, B = 17.9 and 21.3) have the same redshifts within the relatively large uncertainty, ∆vA−B = −1100±1500 km s, of the observations. The quasars are most likely spa...

Based on 5344 quasar spectra taken from the SDSS Data Release 2, the dependences of various emission-line flux ratios on redshift and quasar luminosity are investigated in the ranges 2.0 ≤ z ≤ 4.5 and −24.5 ≥ MB ≥ −29.5. We show that the emission lines in the composite spectra are fitted better with power-law profiles than with double Gaussian or modified Lorentzian profiles, and in particular ...

Black holes with masses Mbh ∼ 10M⊙ dominate the accretion history of the Universe. These black hole masses are typical of those found in radio-selected galaxies today, suggesting that the giant elliptical hosts of low redshift radio galaxies were the hosts of powerful, mostly radio-quiet, quasars in the high redshift Universe. The reason that all radio galaxies are found in such hosts may be th...

We present Hubble Space Telescope images and 2 years of optical photometry of the quadruple quasar HE 0435–1223. The time delays between the intrinsic quasar variations are ∆t AD = −14.37

We have used far-infrared data from IRAS, ISO, SWIRE, SCUBA and MAMBO to constrain statistically the mean far-infrared luminosities of quasars. Our quasar compilation at redshifts 0 < z < 6.5 and I-band luminosities −20 < IAB < −32 is the first to distinguish evolution from quasar luminosity dependence in such a study. We carefully cross-calibrate IRAS against Spitzer and ISO, finding evidence ...

We present the discovery of five quasars at z ∼ 6 selected from 260 deg of the Sloan Digital Sky Survey (SDSS) southern survey, a deep imaging survey obtained by repeatedly scanning a stripe along the Celestial Equator. The five quasars with 20 < zAB < 21 are 1–2 magnitudes fainter than the luminous z ∼ 6 quasars discovered in the SDSS main survey. One of them was independently discovered by th...