Related papers: What drives the Quasar Main Sequence?

Both the Fe II UV emission in the 2000- 3000 A region [Fe II (UV)] and resonance emission line complex of Mg II at 2800 A are prominent features in quasar spectra. The observed Fe II UV/ Mg II emission ratios have been proposed as means to…

In previous studies, it has been shown that the long term time average jet power, $\overline{Q}$, is correlated with the spectral index in the extreme ultraviolet (EUV), $\alpha_{EUV}$ (defined by $F_{\nu} \sim \nu^{-\alpha_{EUV}}$ computed…

Recently some pessimism has been expressed about our lack of progress in understanding quasars over the 50+ year since their discovery. It is worthwhile to look back at some of the progress that has been made - but still lies under the…

We obtained 0.8-2.4 micron spectra at a resolution of 320 km/s of four narrow-line Seyfert 1 galaxies in order to study the near-infrared properties of these objects. We focus on the analysis of the FeII emission in that region and the…

Context. Very high-energy (VHE) $\gamma$-ray measurements of distant TeV blazars can be nicely explained by TeV spectra induced by ultra high-energy cosmic rays. Aims. We develop a model for a plausible origin of hard spectra in distant TeV…

We present near-infrared spectroscopy of the NLS1 galaxy PHL1092 (z=0.394), the strongest FeII emitter ever reported, combined with optical and UV data. We modeled the continuum and the broad emission lines using a power-law plus a black…

The origin and evolution of spectral curvature in blazar spectral energy distribution (SED) is still unclear. Since the observed SED curvature is related to an intrinsic curvature in emitting electron energy distribution (EED), we study…

Determining black hole masses and accretion rates with better accuracy and precision is crucial for understanding quasars as a population. These are fundamental physical properties that underpin models of active galactic nuclei. A primary…

We explore the influence of optical Fe II quasi-continuum on the measured spectral parameters in the 4150-5500 A range for the spectra of Type 1 active galactic nuclei (AGNs). We assume that the broad line region is composed of two…

Broad emission lines in active galactic nuclei (AGNs) mainly arise from gas photoionized by continuum radiation from an accretion disk around a central black hole. The shape of the broad-line profile, described by ${\cal D}_{_{\rm…

Eddington ratio is a paramount parameter governing the accretion history and life cycles of Active Galactic Nuclei (AGNs). This short review presents a multi-faceted view of the importance of the Eddington ratio spanning varied AGN studies.…

Context:Quasars radiating at extreme Eddington ratios (xA) are likely a prime mover of galactic evolution and have been hailed as potential distance indicators. Their properties are still scarcely known. Aims:We test the effectiveness of…

The well-documented E1 relationships are first extended to infrared color $\alpha(60,25)$ and flux ratio [OIII]/H$\beta_{\rm{n}}$ by comparing emission line properties to continuum properties in infrared wavelength. Both direct correlations…

In the context of AGN unification scheme rapid variability properties play an important role in understanding any intrinsic differences between sources in different classes. In this respect any clue based on spectral properties will be very…

Quasars accretion models predict a broad range of optical and ultraviolet properties that depend primarily on black hole mass and accretion rate. Yet, most optically selected luminous quasars display strikingly similar continuum spectra. We…

Understanding the Fe II emission from Active Galactic Nuclei (AGN) has been a grand challenge for many decades. The rewards from understanding the AGN spectra would be immense, involving both quasar classification schemes such as…

Broad emission lines is a prominent property of type I quasi-stellar objects (QSOs). The origin of the Baldwin effect for \civ $\lambda1549~$\AA\ broad emission lines, i.e., the luminosity dependence of the \civ equivalent width (EW), is…

We identify a correlation space involving optical and UV emission line parameters as well as the soft X-ray spectral index that provides optimal discrimination between all principal classes of active galactic nuclei. Most of the sources in…

The width of the broad H-beta emission line is the primary defining characteristic of the NLS1 class. This parameter is also an important component of Boroson and Green's optical Eigenvector 1 (EV1), which links steeper soft X-ray spectra…

We report on a spectral principal component analysis (SPCA) of a sample of 816 quasars, selected to have small Fe II velocity shifts with spectral coverage in the rest wavelength range 3500--5500 \AA. The sample is explicitly designed to…