We have used the WGA catalog of ROSAT PSPC X-ray sources to study the X-ray spectrum of about 500 quasars in the redshift interval 0.1–4.1, detected with a signal to noise better than 7. We have parameterized the PSPC spectrum in terms of two ‘effective energy spectral indices’, αS (0.1-0.8 keV), and αH (0.42.4 keV), which allows for the different Galactic NH along the quasars line of sight. We...

We present the results of a deep K-band imaging study which reveals the host galaxies around a sample of 14 luminous radio-quiet quasars. The K-band images, obtained at UKIRT, are of sufficient quality to allow accurate modelling of the underlying host galaxy. Initially, the basic structure of the hosts is revealed using a modified Clean deconvolution routine optimised for this analysis. Two of...

We have combined a sample of 44 984 quasars, selected from the Sloan Digital Sky Survey (SDSS) Data Release 3, with the FIRST radio survey. Using a novel technique where the optical quasar position is matched to the complete radio environment within 450, we are able to characterize the radio morphological make-up of what is essentially an optically selected quasar sample, regardless of whether ...

We have examined the occurrence of Extremely Red Objects (EROs) in the fields of 13 luminous quasars (11 radio-loud and two radio-quiet) at 1.8 < z < 3.0. The average surface density of Ks ≤ 19 mag EROs is two-three times higher than in large, random-field surveys, and the excess is significant at the ≈ 3σ level even after taking into account that the ERO distribution is highly inhomogeneous. T...

Type 2 quasars are luminous Active Galactic Nuclei whose central engines are seen through large amounts of gas and dust. We present Spitzer spectra of twelve type 2 quasars selected on the basis of their optical emission line properties. Within this sample, we find a surprising diversity of spectra, from those that are featureless to those showing strong PAH emission, deep silicate absorption a...

Considering that quasars evolve into normal galaxies the average expansion velocity of matter in quasars (or galaxies) can be estimated approximately. Such velocity makes us to see the light of quasars slightly Doppler shifted which explains the misleading variation of the fine structure constant. There have been reports 1−4 in the literature proposing a time variation of the fine structure con...

Of 90 extragalactic objects chosen from the I RAS catalog on the basis of brightness at 60 μm and "warm" infrared color [f.(25 μm)lfv(60 μm) > 0.2], 12 have luminosities characteristic of quasars. These 12 ultraluminous objects have Seyfert spectra, and nine of them show morphological evidence for recent collisions or mergers-they plausibly represent a transition stage between cooler ultralumin...

We present Hubble Space Telescope ACS images of 13 dust-reddened type 1 quasars selected from the FIRST/ 2MASS Red Quasar Survey. These quasars have high intrinsic luminosities after correction for dust obscuration ( 23:5 MB 26:2 from K-magnitude). The images show strong evidence of recent or ongoing interaction in 11 of the 13 cases, even before the quasar nucleus is subtracted. None of the ho...

Observations with the Wide-Field/Planetary Camera-2 of the Hubble Space Telescope (HST) are presented for three radio-loud quasars: 3C 48 (z = 0.367), B2 1425+267 (z = 0.366), and 3C 345 (z = 0.594). All three quasars have luminous (∼ 4× L) galaxies as hosts, which are either elliptical (B2 1425+267 and 3C 345) or interacting (3C 48), and all hosts are 0.5 − 1.0 mag bluer in (V −I) than other g...