相关论文: The Distribution and Evolution of Quasar Proximity…
The spectrum of the quasar Q0055-269 ($z=3.66$) has been observed at the resolution of 14 km s$^{-1}$ in the wavelength interval 4750--6300 \AA. We give a list of Lyman$-\alpha$ lines and metal-line systems for which column densities and…
We present simulations of quasar colors, magnitudes, and numbers at redshifts 5<z<10 based on our discovery of ten new high-redshift quasars and the cloning of lower redshift Sloan Digital Sky Survey (SDSS) quasars. The ten quasars have…
Study of Lyman-alpha absorption lines in the spectra of double line of sight (DLOS) quasars holds the promise of diagnosing the nature of the structures that give rise to Lyman-alpha absorption. Based on simulations of DLOS with various…
We present the final results from our survey of luminous $z \sim $ 5.5 quasars. This is the first systematic quasar survey focusing on quasars at $z \sim$ 5.5, during the post-reionization epoch. It has been challenging to select quasars at…
We study the effects of box size on ENZO simulations of the intergalactic medium (IGM) at z = 2. We follow statistics of the cold dark matter (CDM) and the Lya absorption. We find that the larger boxes have fewer pixels with significant…
A model of Lyman limit QSO absorption systems is investigated where they are produced in gaseous galactic halos with a two-phase structure: a hot phase at the halo virial temperature in approximate pressure equilibrium, and a cold,…
We briefly discuss the relevance of Lyman alpha forest observations for measuring cosmological parameters, comparing the properties of high z QSO spectra with those of artifical spectra from hydrodynamic simulations, based on hierarchical…
We present high-resolution zoom-in simulations of molecular clouds exposed to an interstellar radiation field and cosmic ray ionisation rate up to 1000 times stronger than that of the solar neighbourhood. We detail the evolution of the…
The spatial distribution of Ly-alpha forest absorption systems towards ten QSOs has been analysed to search for large-scale structure over the redshift range 2.2 < z < 3.4. The QSOs form a closely spaced group on the sky and are…
In this work, I investigate the properties of Lyman limit systems (LLSs) using state-of-the-art zoom-in cosmological galaxy formation simulations with on the fly radiative transfer, which includes both the cosmic UV background (UVB) and…
We use hydrodynamic cosmological simulations to study damped Lyman-alpha (DLA) and Lyman limit (LL) absorption at redshifts z=2-4 in five variants of the cold dark matter scenario. Our standard simulations resolve the formation of dense…
Discovery of the cosmic reionization epoch would represent a significant milestone in cosmology. We present Keck spectroscopy of the quasar SDSS 1044-0125, at z = 5.73. The spectrum shows a dramatic increase in the optical depth at observed…
The nature of the galaxies that give rise to absorption lines, such as damped Lyman-alpha systems (DLAs) or strong MgII lines, in quasar spectra is difficult to investigate in emission. Taking advantage of the total absorption of the QSO…
We have conducted an optical/near-infrared study of the environments of radio-loud quasars (RLQs) at redshifts z=0.6-2. In this paper we discuss the sample selection and observations for the z=1-2 subsample and the reduction and cataloguing…
Interferometry of the cosmic 21-cm signal is set to revolutionize our understanding of the Epoch of Reionization (EoR), eventually providing 3D maps of the early Universe. Initial detections however will be low signal-to-noise, limited by…
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…
Comparison of the observed evolution of the Ly-alpha transmitted flux in the spectra of four highest redshift quasars discovered by SLOAN survey with the theoretical prediction for this evolution based on the state-of-the-art numerical…
The inhomogeneous cosmological reionization process leaves tangible imprints in the intergalactic medium down to z=4-5. The Lyman-alpha forest flux power spectrum provides a potentially powerful probe of the epoch of reionization. With the…
We have constructed a sample of 29 close projected quasar pairs where the background quasar spectrum reveals absorption from optically thick HI gas associated with the foreground quasar. These unique sightlines allow us to study the quasar…
Determining when and how the first galaxies reionized the intergalactic medium (IGM) promises to shed light on both the nature of the first objects and the cosmic history of baryons. Towards this goal, quasar absorption lines play a unique…