Related papers: Quasars in a merger model: comparison with the obs…
We link the evolution of the galaxies in the hierarchical clustering scenario with the changing accretion rates of cold gas onto the central massive black holes that power the quasars. We base on galaxy interactions as main triggers of…
By comparing the results of numerical microlensing simulations to the observed long-term variability of quasars, strong upper limits on the cosmological density of compact objects in the mass range 0.01 to 0.0001 solar masses may be…
We consider the impact of quasar outflows on structure formation. Such outflows are potentially more important than galactic winds, which appear insufficient to produce the level of preheating inferred from X-ray observations of galaxy…
We have derived the quasar luminosity function assuming that the quasar activity is driven by a thermal-viscous unstable accretion disk around a supermassive black hole. The instabilities produce large amplitude, long-term variability of a…
We show that current clustering observations of quasars and luminous AGN can be explained by a merger model augmented by feedback from outflows. Using numerical simulations large enough to study clustering out to 25 comoving h^{-1} Mpc, we…
We investigate the distribution of companion galaxies around quasars using {\em Hubble Space Telescope} ({\em HST}) Advanced Camera for Surveys Wide Field Camera (ACS/WFC) archival images. Our master sample contains 532 quasars which have…
Many gravitationally lensed quasars exhibit flux ratio "anomalies" that cannot be explained under the hypothesis that the lensing potential is smooth on scales smaller than one kpc. Micro-lensing by stars is a natural source of granularity…
We investigate the environments of quasars such as number distribution of galaxies using a semi-analytic model which includes both galaxy and quasar formations based on the hierarchical clustering scenario. We assume that a supermassive…
We study the dependence of the number density and properties of quasars on the background galaxy density using the currently largest spectroscopic datasets of quasars and galaxies. We construct a galaxy number density field smoothed over…
We study the observational signatures of a potential population of low-luminosity quasars at high redshifts in a LambdaCDM cosmology. We derive the evolution of the quasar luminosity function at fainter luminosities and higher redshifts…
We place a limit on the logarithmic slope of the luminous quasar luminosity function at z~6 of beta>-3.0 (90%) using gravitational lensing constraints to build on the limit of beta>-3.3 (90%) derived from an analysis of the luminosity…
We introduce a phenomenological investigation of the evolution and large scale distribution of quasars using a modified version of the Field and Colgate gravitational contraction model for proto-galaxies. By studying the distribution of…
Via the magnification bias, gravitational lensing by large-scale structures causes angular cross-correlations between distant quasars and foreground galaxies on angular scales of arc minutes and above. We investigate the three-point…
We investigate the characteristic radiative efficiency \epsilon, Eddington ratio \lambda, and duty cycle P_0 of high-redshift active galactic nuclei (AGN), drawing on measurements of the AGN luminosity function at z=3-6 and, especially, on…
There is controversy about the measurement of statistical associations between bright quasars and faint, presumably foreground galaxies. We look at the distribution of galaxies around an unbiased sample of 63 bright, moderate redshift…
Recent observations have found that many $z\sim 6$ quasar fields lack galaxies. This unexpected lack of galaxies may potentially be explained by quasar radiation feedback. In this paper I present a suite of 3D radiative transfer…
We explore the properties of galaxies in the proximity (within a $\sim$2 Mpc radius sphere) of Type I quasars at 0.1<z<0.35, to check whether and how an active galaxy influences the properties of its neighbors. We further compare these with…
We combine photometry from the UDS, and CANDELS UDS and CANDELS GOODS-S surveys to construct the galaxy stellar mass function probing both the low and high mass end accurately in the redshift range 0.3<z<3. The advantages of using a…
Last year (2013) was more or less the 50th anniversary of the discovery of quasars. It is an interesting time to review what we know (and don't know) about them both empirically and theoretically. These compact sources involving line…
Quasars are the visible signatures of super-massive black holes in the centres of distant galaxies. It has been suggested that quasars are formed during ``major merger events'' when two massive galaxies collide and merge, leading to the…