相关论文: The Epoch of Helium Reionization

A variety of observations now indicate that intergalactic helium was fully ionized by z~3. The most recent measurements of the high-redshift quasar luminosity function imply that these sources had produced ~2.5 ionizing photons per helium…

The reionization of the second electron of helium (HeII) leaves important imprints on the thermal and ionization state of the intergalactic medium (IGM). Observational evidence suggests that HeII reionization ended at $z \simeq 3$ due to…

The radiation background above the ionization edge of HeII varies strongly during and after helium reionization, because the attenuation length of such photons is relatively short (<40 Mpc) and because the ionizing sources (quasars) are…

Quasars that allow the study of IGM He II are very rare, since they must be at high redshift along sightlines free of substantial hydrogen absorption, but recent work has dramatically expanded the number of such quasars known. We analyze…

We have run a new suite of simulations that solve hydrodynamics and radiative transfer simultaneously to study helium II reionization. Our suite of simulations employs various models for populating quasars inside of dark matter halos, which…

The ionizing background determines the ionization balance and the thermodynamics of the cosmic gas. It is therefore a fundamental ingredient to theoretical and empirical studies of both the IGM and galaxy formation. We present here a new…

The full reionization of intergalactic helium was a major event in the history of the IGM, and UV observations of the He II Gunn-Peterson trough allow us to characterize the end of this process at z~3. Due to intervening hydrogen…

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…

Interpretation of He II Ly{\alpha} absorption spectra after the epoch of He II reionization requires knowledge of the He II ionizing background. While past work has modelled the evolution of the average background, the standard cosmological…

We study the ionization and thermal evolution of the intergalactic medium during the epoch of \heii reionization by means of radiation hydrodynamical cosmological simulations. We post-process baryonic density fields from a standard…

We compute the reionization histories of hydrogen and helium due to the ionizing radiation fields produced by stars and quasars. For the quasars we use a model based on halo-merger rates that reproduces all known properties of the quasar…

The reionization of the second electron of helium shapes the physical state of intergalactic gas at redshifts between 2 < z < 5. Because performing full in situ radiative transfer in hydrodynamic simulations is computationally expensive for…

Using hydrodynamical simulations coupled to a radiative transfer code, we study the additional heating effects in the intergalactic medium (IGM) produced by $z\sim 6$ quasars in their near-zones. If helium is predominantly in HeII to begin…

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…

The incorporation of radiative transfer effects into cosmological hydrodynamical simulations is essential for understanding how the intergalactic medium (IGM) makes the transition from a neutral medium to one that is almost fully ionized.…

Using radiative transfer calculations and cosmological simulations of structure formation, we study constraints that can be placed on the nature of the cosmic ultraviolet (UV) background in the redshift interval 2.5< z <5. Our approach…

Despite decades of effort, the timing and duration of He II reionization, as well as its morphology and the properties of the quasars believed to drive it, are still not well constrained. In this paper we present a new method to study both…

Recently, models of the quasar luminosity function (QLF) rooted on large observational compilations have been produced that, unlike their predecessors, feature a smooth evolution with time. This bypasses the need to assume an ionizing…

We present measurements of the large-scale (~40 comoving Mpc) effective optical depth of HeII Ly$\alpha$ absorption, $\tau_{\rm eff}$, at 2.54<z<3.86 toward 16 HeII-transparent quasars observed with the Cosmic Origins Spectrograph (COS) on…

The expansion of the Universe leads to a rapid drop in the mean hydrogen Ly-alpha opacity tau of the intergalactic medium (IGM), tau (1+z)^{3.8}, between redshifts 4 and 3. Measurements of the temperature evolution of the IGM and of the He…