Related papers: Quasars with Anomalous H\beta\ Profiles I: Demogra…
We present an X-ray and multiwavelength study of 33 weak emission-line quasars (WLQs) and 18 quasars that are analogs of the extreme WLQ, PHL 1811, at z ~ 0.5-2.9. New Chandra 1.5-9.5 ks exploratory observations were obtained for 32 objects…
We report the results from Chandra and XMM-Newton observations of a sample of 10 type 1 quasars selected to have unusual UV emission-line properties (weak and blueshifted high-ionization lines; strong UV Fe emission) similar to those of PHL…
Broad Fe II emission is a prominent feature of the optical and ultraviolet spectra of quasars. We report on a systematical investigation of optical Fe II emission in a large sample of 4037 z < 0.8 quasars selected from the Sloan Digital Sky…
Associated absorption lines (AALs) in quasar spectra are valuable probes of the gas kinematics and physical conditions in quasar environments. The host galaxies are by definition in an active evolution stage that might involve large-scale…
Surveys have shown radio-loud (RL) quasars constitute 10%-15% of the total quasar population and rest are radio-quiet (RQ). However, it is unknown if this radio-loud fraction (RLF) remains consistent among different parameter spaces. This…
[Abridged] We present new VLT ISAAC spectra for 30 quasars, which we combine with previous data to yield a sample of 53 intermediate redshift (z ~ 0.9 - 3.0) sources. The sample is used to explore properties of prominent lines in the Hbeta…
With close pairs of quasars at different redshifts, a background quasar sightline can be used to study a foreground quasar's environment in absorption. We use a sample of 650 projected quasar pairs to study the HI Lya absorption transverse…
We perform a systematic search for sub-parsec binary supermassive black holes (BHs) in normal broad line quasars at z<0.8, using multi-epoch SDSS spectroscopy of the broad Hbeta line. Our working model is that: only one of the two BHs in…
We use archival WISE and Spitzer photometry to derive optical line fluxes for a sample of distant quasars at z ~6. We find evidence for exceptionally high equivalent width [OIII] emission (rest-frame EW ~400 {\AA}) similar to that inferred…
A quasar main sequence is widely believed to reveal itself through objects represented in a plane spanned by two parameters: the full-width at half-maximum (FWHM) of H$\beta{}$, and the ratio of Fe II to H$\beta{}$ equivalent width. This…
There is evidence from radio-loud quasars to suggest that the distribution of the H$\beta$ broad emission line (BEL) gas is arranged in a predominantly planar orientation, and this result may well also apply to radio-quiet quasars. This…
The concept of the quasar main sequence is very attractive since it stresses correlations between various parameters and implies the underlying simplicity. In the optical plane defined by the width of the H\{beta} line and the ratio of the…
Based on a new spectroscopic sample observed using the WHT, we examine the kinematic properties of the various emission line regions in narrow line Seyfert 1 galaxies (NLS1s) by modelling their profiles using multiple component fits. We…
We present a catalog of broad H$\beta$ variability properties for all spectra of quasars with $z<0.8$ and at least two observations included in the Sloan Digital Sky Survey (SDSS) Data Release 16 quasar catalog. For each spectrum, we…
Narrow Line Seyfert 1 galaxies represent a distinct category in the larger family of Type 1 Active Galactic Nuclei. The occurrence of emission line profiles not broader than 2000 km/s, combined with luminosity estimates comparable to those…
Type II quasars are the long-sought luminous analogs of type II (narrow emission line) Seyfert galaxies, suggested by unification models of active galactic nuclei (AGN) and postulated to account for an appreciable fraction of the cosmic…
Infrared spectroscopy of the H-alpha emission lines of a sub-sample of 19 high-redshift (0.8 < z < 2.3) Molonglo quasars, selected at 408 MHz, is presented. These emission lines are fitted with composite models of broad and narrow emission,…
In this Letter, the properties of the extended radio emission form SDSS DR7 quasars with $0.4<z<0.8$ is studied. This low redshift sample is useful since any corresponding FIRST radio observations are sensitive enough to detect extended…
We conduct the first systematic survey of a total of eleven optical coronal lines in the spectra of a large sample of low redshift (z < 0.8) Type 1 quasars observed by the Sloan Digital Sky Survey (SDSS). We find that strong coronal line…
IZw1 is the prototype narrow line quasar. This type of AGNs show a number of common peculiar characteristics whose physical origin is not yet well understood. Here, I review the results of a detailed study by Laor et al. (1997b) of the UV…