We investigate the MBH−σ∗ relation for radio-loud quasars with redshift z < 0.83 in Data Release 3 of the Sloan Digital Sky Survey (SDSS). The sample consists of 3772 quasars with better model of Hβ and [O III] lines and available radio luminosity, including 306 radio-loud quasars, 3466 radio-quiet quasars with measured radio luminosity or upper-limit of radio luminosity (181 radio-quiet quasar...

We present imaging and spectroscopic observations for six quasars at z ≥ 5.9 discovered by the CanadaFrance High-z Quasar Survey (CFHQS). The CFHQS contains sub-surveys with a range of flux and area combinations to sample a wide range of quasar luminosities at z ∼ 6. The new quasars have luminosities 10 to 75 times lower than the most luminous SDSS quasars at this redshift. The least luminous q...

We present five X-ray quasars behind the Small Magellanic Cloud, increasing the number of known quasars behind the SMC by ∼40%. They were identified via follow-up spectroscopy of serendipitous sources from the Chandra X-ray Observatory matched with objects from the OGLE database. All quasars lie behind dense parts of the SMC, and could be very useful for proper motion studies. We analyze X-ray ...

Wang et al. (2006) estimated an average radiative efficiency of 30%–35% for quasars at moderate redshift. We find that their method is not independent of quasar lifetimes and thus that quasars do not necessarily have such high efficiencies. Nonetheless, it is possible to derive interrelated constraints on quasar lifetimes, Eddington ratios, and radiative efficiencies of supermassive black holes...

This paper reports the X-ray spectral analysis of 5 high-redshift (z≥2) radio-quiet quasars observed by ASCA. A simple power law continuum plus cold Galactic absorption model well fits all the spectra (tipically between ∼ 2–30 keV in the sources frame). Neither the X–ray spectral hardening, attributed to a reflection component and observed in Seyfert galaxies, nor the excess absorption previous...

The [O II] λ3727 line, a commonly used estimator of star formation rate in extragalactic surveys, should be an equally effective tracer of star formation in the host galaxies of quasars, whose narrow-line regions are expected to produce weak low-ionization emission. Quasar spectra generally show little or no [O II] emission beyond that expected from the active nucleus itself. The inferred star ...

Optical spectroscopic data are presented here for quasars from the Molonglo Quasar Sample (MQS), which forms part of a complete survey of 1-Jy radio sources from the Molonglo Reference Catalogue. The combination of low-frequency selection and complete identifications means that the MQS is relatively free from the orientation biases which affect most other quasar samples. To date, the sample inc...

Near-infrared measurements have been obtained of 30 quasars originally found serendipitously as x-ray sources in fields of other objects. The observations show that the infrared characteristics of these quasars do not differ significantly from those of quasars selected by other criteria. Because this x-ray-selected sample is subject to different selection biases than previous radio and optical ...

We present VLT/ISAAC near-infrared imaging of the host galaxies of 15 low luminosity quasars at 1 < z < 2. This work complements our studies to trace the cosmological evolution of the host galaxies of high luminosity quasars. The radioloud (RLQ) and radio-quiet (RQQ) quasars have similar distribution of redshift and luminosity, and together the high and low luminosity quasars cover a large rang...

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 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 FR I/FR II break. Consequently, low power radio quasars would either be clas...