Related papers: Spectral Evolution in High Redshift Quasars from t…
Many years of study have failed to conclusively establish relations between a quasar's spectral energy distribution (SED) and the emission lines it is thought to produce. This is at least partially due to the lack of well-observed SEDs. We…
We report on our XMM observations of the high redshift quasars BR 2237--0607 (z=4.558) and BR 0351--1034 (z=4.351), together with 14 other z>4 objects found in the XMM public archive. Contrary to former reports, we do not find high redshift…
We report on three redshift $z>2$ quasars with dramatic changes in their C IV emission lines, the first sample of changing-look quasars (CLQs) at high redshift. This is also the first time the changing-look behaviour has been seen in a…
We have searched in the XMM-Newton public archive for quasars in the Sloan Digital Sky Survey (SDSS) First Data Release (DR1), and found 55 lying in the field of a XMM-Newton observation with exposure times >20 ksec (as of August, 2004).…
Different works have recently found an increase of the average X-ray-to-radio luminosity ratio with redshift in the blazar population. We evaluate here whether the inverse Compton interaction between the relativistic electrons within the…
We present a new approach to capturing the broad diversity of emission line and continuum properties in quasar spectra. We identify populations of spectrally similar quasars through pixel-level clustering on 12,968 high signal-to-noise…
We have observed a sample of 22 luminous quasars, in the range 2.0<z<2.5, at 1.6 microns with the near-infrared (NIR) spectrograph FSPEC on the Multiple Mirror Telescope. Our sample contains 13 radio-loud and 9 radio-quiet objects. We have…
We construct mean spectral energy distributions (SEDs) for a substantial sample of 56,969 Sloan Digital Sky Survey DR16 quasars with $z < 0.75$, utilizing multiwavelength data from the mid-infrared (MIR) to ultraviolet (UV). These SEDs are…
We present an analysis of the mid-infrared (MIR) and optical properties of type 1 (broad-line) quasars detected by the Spitzer Space Telescope. The MIR color-redshift relation is characterized to z=3, with predictions to z=7. We demonstrate…
Quasars serve as important cosmological probes and constructing accurate luminosity relations for them is essential for their use in cosmology. If the coefficients of quasar's luminosity relation vary with redshift, it could introduce…
We construct a parametric SED model which is able to reproduce the average observed SDSS-UKIDSS-WISE quasar colours to within one tenth of a magnitude across a wide range of redshift $(0<z<5)$ and luminosity $(-22>M_i>-29)$. This model is…
A minority of the optically selected quasar population are red at optical wavelengths due to the presence of dust along the line-of-sight. A key focus of many red quasar studies is to understand their relationship with the overall quasar…
We compare, with data from the quasars, the Hubble parameter measurements, and the Pantheon+ type Ia supernova, three different relations between X-ray luminosity ($L_X$) and ultraviolet luminosity ($L_{UV}$) of quasars. These three…
We present a statistical analysis of the final lens sample from the Sloan Digital Sky Survey Quasar Lens Search (SQLS). The number distribution of a complete subsample of 19 lensed quasars selected from 50,836 source quasars is compared…
We describe the application of non-negative matrix factorisation to generate compact reconstructions of quasar spectra from the Sloan Digital Sky Survey (SDSS), with particular reference to broad absorption line quasars (BALQSOs). BAL…
Faint quasar surveys are necessary complements to bright quasar surveys to remove the degeneracy between redshift and luminosity inherent in any single magnitude-limited sample. I discuss two ongoing surveys for faint quasars at 3.3<z<5 and…
Accretion processes in quasars and active galactic nuclei are still poorly understood, especially as far as the connection between observed spectral properties and physical parameters is concerned. Quasars show an additional degree of…
We find that the Fe III$\lambda\lambda$2039-2113 spectral feature in quasars appears systematically redshifted by amounts accountable under the hypothesis of gravitational redshift induced by the central supermassive black hole. Our…
We present a method for studying the proximity effect and the density structure around redshift z=2-3 quasars. It is based on the probability distribution of Lyman-alpha pixel optical depths and its evolution with redshift. We validate the…
We present a new measurement of the optical Quasar Luminosity Function (QLF), using data from the Sloan Digital Sky Survey-III: Baryon Oscillation Spectroscopic Survey (SDSS-III: BOSS). From the SDSS-III Data Release Nine (DR9), we select a…