Related papers: Modeling the HeII Transverse Proximity Effect: Con…
We analyse the proximity zone of the intergalactic matter around high-redshift quasars in a cosmological environment. In a box of 64 h-1 Mpc base length we employ dark matter only simulations. For estimating the hydrogen temperature and…
We study the reionization of Helium II by quasars using a numerical approach that combines 3D radiative transfer calculations with cosmological hydrodynamical simulations. Sources producing the ionizing radiation are selected according to…
We point out the peculiarities of the line of sight of Q0302-003 which was recently used to estimate the He II opacity at $z \sim 3.285$. This line of sight contains a large void in Lyman $\alpha$ clouds, in the region used for the He II…
We present evidence for a skewed distribution of UV FeII emission in quasars within candidate overdense regions spanning spatial scales of ~ 50 Mpc at 1.11 < z < 1.67, compared to quasars in field environments at comparable redshifts. The…
The UV radiation from high redshift quasars causes a local deficit in the neutral hydrogen absorption (Lyman-alpha forest) in their spectra, known as the proximity effect. Measurements from small samples of tens to hundreds of quasars have…
Absorption along quasar sightlines remains among the most sensitive direct measures of HeII reionization in much of the intergalactic medium (IGM). Until recently, fewer than a half-dozen unobscured quasar sightlines suitable for the HeII…
We present a new HST/STIS spectrum of the z=3.18 quasar PKS 1935-692 and summarize the spectral features shortwards of 304A in the rest frame likely to be caused by foreground HeII Lyman-alpha absorption. In accord with previous results on…
We introduce a new project to understand helium reionization using fully coupled $N$-body, hydrodynamics, and radiative transfer simulations. This project aims to capture correctly the thermal history of the intergalactic medium (IGM) as a…
A toy model is developed to understand how the spatial distribution of fluorescent emitters in the vicinity of bright quasars could be affected by the geometry of the quasar bi-conical radiation field and by its lifetime. The model is then…
Absorption spectra of high redshift quasars exhibit an increasingly thick Ly-alpha forest towards z~6. However, the interpretation of these spectra is complicated by the fact that the Ly-alpha optical depth is already large for neutral…
We present an investigation of the interdependence of the optical-to-X-ray spectral slope ($\alpha_{\rm ox}$), the HeII equivalent-width (EW), and the monochromatic luminosity at 2500 Angstroms ($L_{2500}$). The values of $\alpha_{\rm ox}$…
Observations from the HUT and the HST have recently detected HeII absorption along the lines of sight to two high redshift quasars. We use cosmological simulations with gas dynamics to investigate HeII absorption in the cold dark matter…
High-redshift quasars (z >~ 6) drive ionization fronts into the intergalactic medium (IGM). If the thickness of the front can be measured, it can provide a novel constraint on the ionizing spectral energy distribution (SED). Here we follow…
We present a study of the impact of a bright quasar on the redshifted 21cm signal during the Epoch of Reionization (EoR). Using three different cosmological radiative transfer simulations, we investigate if quasars are capable of…
Measuring the response of the intergalactic medium to a blast of ionizing radiation allows one to infer the physical properties of the medium and, in principle, the lifetime and isotropy of the radiating source. The most sensitive such…
The Ly-alpha absorption spectrum of the highest redshift quasars indicates that they are surrounded by giant HII regions, a few Mpc in size. The neutral gas around these HII regions should emit 21cm radiation in excess of the Cosmic…
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…
The ultraviolet spectrum (1145--1720A) of the distant quasar Q 0302--003 (z=3.286) was observed at 1.8A resolution with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. A total integration time of 23,280 s was…
Recent observations suggest that helium became fully ionized around redshift z ~ 3. The HeII optical depth derived from the Lyman-alpha forest decreases substantially from this period to z ~ 2; moreover, it fluctuates strongly near z ~ 3…
We present a new method to directly map the neutral-hydrogen distribution during the reionization epoch and to constrain the emission properties of the highest-redshift quasars (QSOs). As a tracer of HI, we propose to use the Ly-alpha…