We have performed quasi-simultaneous radio flux density measurements at 2.7 and 10 GHz for all PG quasars with radio flux densities between 4-200 mJy. We find that a large fraction of these sources are variable, flat-spectrum quasars. This brings the total fraction of flat-spectrum quasars with a ratio between radio and optical flux of R > 10 — a value previously used to define a radio-loud qua...

We have performed quasi-simultaneous radio ux density measurements at 2.7 and 10 GHz for all PG quasars with radio ux densities between 4-200 mJy. We nd that a large fraction of these sources are variable, at-spectrum quasars. This brings the total fraction of at-spectrum quasars with a ratio between radio and optical ux of R > 10 | a value previously used to deene a radio-loud quasar | to 40% ...

If the unexpectedly high frequency of quasar pairs with very different component redshifts is due to the lensing of a population of background quasars by the foreground quasar, typical lens masses must be ∼ 10M⊙ and the sum of all such quasar lenses would have to contain ∼ 0.005 times the closure density of the Universe. It then seems plausible that a very high fraction of all ∼ 10M⊙ gravitatio...

We cross-correlate the SDSS DR3 quasar sample with FIRST and the Vestergaard et al. black hole (BH) mass sample to compare the mean accretion histories of optical and radio quasars. We find significant statistical evidence that radio quasars have a higher mean Eddington ratio λ at z > 2 with respect to optical quasars, while the situation is clearly reverse at z < 1. At z > 2 radio quasars happ...

This study provides new arguments for the existence of local quasars, i.e. quasars in the vicinity of low redshift galaxies. Local quasars are probably ejected from respective parent galaxy. The sample includes 74 quasars in the vicinity of 8 different galaxies. Assuming for quasars the same distances from the observer, as for their respective parent galaxy, simple calculations lead to the quas...

Using mid-infrared and radio criteria, we select a sample of candidate z ∼ 2 obscured quasars. Optical spectroscopy confirms about half of these as type-2 quasars, and modelling the population suggests 50-80% of the quasars are obscured. We find some flat radio spectrum type-2 quasars, and tentative evidence for obscuration unrelated to the torus. Using a similar sample, we also find evidence f...

Using mid-infrared and radio criteria, we select a sample of candidate z ∼ 2 obscured quasars. Optical spectroscopy confirms about half of these as type-2 quasars, and modelling the population suggests 50-80% of the quasars are obscured. We find some flat radio spectrum type-2 quasars, and tentative evidence for obscuration unrelated to the torus. Using a similar sample, we also find evidence f...

We present VLBI (EVN+MERLIN) observations of a sample of three low-redshift radio-intermediate PG quasars (RIQ) with at and variable radio spectrum (III Zw 2, PG 1309+355, PG 2209+184). Their radio-to-optical ux ratio (R) is slightly lower than the average R for steep-spectrum quasars, but their radio spectral properties are those of core-dominated quasars. It was proposed previously that these...