Related papers: Cold Accretion Disks and Lineless Quasars
AGN SEDs generally show a turnover at lambda 1000A, implying a maximal accretion disc (AD) temperature of T_max~50,000K. Massive O stars display a similar T_max, associated with a sharp rise in a line driven mass loss Mdot_wind with…
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…
Quasars accreting matter at very high rates (known as extreme Population A [xA] or super-Eddington accreting massive black holes) provide a new class of distance indicators covering cosmic epochs from the present-day Universe up to less…
Quasars (QSOs) emit an enormous amount of light as a result of the accretion of gas onto supermassive black holes (SMBHs). Thanks to their luminosity, the most distant known QSOs allow us to trace the growth of SMBHs deep into the epoch of…
Using Sloan Digital Sky Survey (SDSS) quasar spectra taken at multiple epochs, we find that the composite flux density differences in the rest frame wavelength range 1300-6000 AA can be fit by a standard thermal accretion disk model where…
We present near-infrared spectroscopy of ten weak emission-line quasars (WLQs) at redshifts of $z\sim2$, obtained with the Palomar 200-inch Hale Telescope. WLQs are an exceptional population of type 1 quasars that exhibit weak or no broad…
We investigate the discrepancy between the predicted size of accretion disks (ADs) in quasars and the observed sizes as deduced from gravitational microlensing studies. Specifically, we aim to understand whether the discrepancy is due to an…
The ionizing continuum shape of quasars is generally not directly observable, but indirect arguments, based on photoionization models and thin accretion disk models suggest that it should peak in the extreme UV, and drop steeply into the…
Strong broad emission lines are the most important signatures of active galactic nuclei. These lines allowed to discover the cosmological nature of quasars, and at present these lines allow for convenient method of weighting the black holes…
Active galactic nuclei (AGN) have been observed to vary stochastically with 10-20 rms amplitudes over a range of optical wavelengths where the emission arises in an accretion disk. Since the accretion disk is unlikely to vary coherently,…
We revisit the spectral appearance of extended self-gravitating accretion disks surrounding compact central objects such as supermassive black holes. Using dust-poor opacities, we show that all optically thick disk solutions possess a…
We identify and characterize a population of luminous dust poor quasars at 0<z<5, similar in photometric properties to the objects found at z>6 previously. This class of active galactic nuclei has been known to show little IR emission from…
Microlensing perturbations to the flux ratios of gravitationally lensed quasar images can vary with wavelength because of the chromatic dependence of the accretion disk's apparent size. Multiwavelength observations of microlensed quasars…
QSO emission-line spectra are compared to predictions based on theoretical ionizing continua of accretion disks. Observed line intensities do not show the expected trend of higher ionization with higher accretion disk temperature as derived…
In a previous paper, Collin & Hur\'e (2001), using a sample of Active Galactic Nuclei (AGN) where the mass has been determined by reverberation studies (Kaspi et al. 2000), have shown that if the optical luminosity is emitted by a steady…
We develop a general method for analyzing the light curves of microlensed quasars and apply it to the OGLE light curves of the four-image lens Q2237+0305. We simultaneously estimate the effective source velocity, the average stellar mass,…
Optical/UV radiation from accretion disks in quasars is likely to be partly scattered by a hot plasma enveloping the disk. We investigate whether the scattering may produce the steep rises in polarization observed blueward of the Lyman…
The thesis concerns the analysis of the Active Galactic Nuclei. These are galaxies with an active core. The most luminous type of Active Galactic Nuclei is Quasar. It contains the supermassive black hole at the center. One of the least…
We analyzed the microlensing of the X-ray and optical emission of the lensed quasar PG 1115+080. We find that the effective radius of the X-ray emission is 1.3(+1.1 -0.5) dex smaller than that of the optical emission. Viewed as a thin disk…
At luminosities below a few percent of Eddington, accreting black holes switch to a hard spectral state which is very different from the soft blackbody-like spectral state that is found at higher luminosities. The hard state is…