相关论文: How exactly did the Universe become neutral?

This letter concentrates on the non-equilibrium evolution of magnetic field structures at the onset of recombination, when the charged particle current densities decay as neutrals are formed. We consider the effect that a decaying magnetic…

I use cosmological simulations that incorporate a physically motivated approximation to three-dimensional radiative transfer that recovers correct asymptotic ionization front propagation speeds for some cosmologically relevant density…

We present the first detailed ab initio quantum mechanical calculations for total and state-specific recombination rate coefficients for e + Ni III --> Ni II. These rates are obtained using a unified treatment for total electron-ion…

We have developed a modular semi-numerical code that computes the time and spatially dependent ionization of neutral hydrogen (HI), neutral (HeI) and singly ionized helium (HeII) in the intergalactic medium (IGM). The model accounts for…

This paper presents a study of the dependence of the simulated intensities of recombination lines from hydrogen and helium atoms on the number of $n\ell$-resolved principal quantum numbers included in the calculations. We simulate hydrogen…

We calculate the ionization cross sections for H, He or Ne atoms using $\nu_e$ and $\bar \nu_e$ scattering at keV energies. Such cross sections are useful for e.g. $\bar \nu_e$-oscillation experiments using a tritium source. Using realistic…

The history of the transition from a neutral intergalactic medium (IGM) to one that is almost fully ionized can reveal the character of cosmological ionizing sources and set important constraints on the stellar birthrate at high redshifts.…

This work presents a Bayesian algorithm to fit the recombination and collisionally excited line spectra of gas photoionized by clusters of young stars. The current model consists in fourteen dimensions: two electron temperatures, one…

We report on measurements of the 4He abundance toward the outer Galaxy HII region S206 with the NRAO Green Bank telescope. Observations of hydrogen and helium radio recombination lines between 8-10 GHz were made toward the peak radio…

We estimate the He II to H I column density ratio, \eta = N(He II)/N(H I), in the intergalactic medium towards the high redshift (z_{em} = 2.885) bright quasar QSO HE 2347-4342 using Voigt-profile fitting of the H I transitions in the Lyman…

In this introductory chapter, we outline expectations for when and how the hydrogen and helium atoms in the universe turned from neutral to ionized, focusing on the earliest, least well understood stages, and emphasizing the most important…

We show that the process of photoionizing a gas of atomic hydrogen and helium by line radiation whose energy is slightly above the helium single-ionization threshold is unstable if the helium fraction by number is less than approximately…

The high ionization level and universal metallicity (1% solar) of the intergalactic gas at redshifts z<5 implies that nonlinear structure had started to form in the universe at earlier times than we currently probe. In Cold Dark Matter…

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 evolution of neutral hydrogen (HI) across redshifts is a powerful probe of cosmology, large scale structure in the universe and the intergalactic medium. Using a data-driven halo model to describe the distribution of HI in the…

The quasi-molecular mechanism of recombination, recently suggested by Kereselidze et al., is a non-standard process where an electron and two neighboring protons in the early universe directly form an ionized hydrogen molecule in a highly…

With the high-resolution spectroscopy now available in the optical and satellite UV, it is possible to determine the neutral/ionized column density ratios for several different elements in a single cloud. Assuming ionization equilibrium for…

The contribution of stars in galaxies to cosmic reionisation depends on the star formation history in the Universe, the abundance of galaxies during reionisation, the escape fraction of ionising photons and the clumping factor of the…

We present a semi-analytic model for the thermal and ionization history of the universe at 1000 >~ z >~ 3. This model incorporates much of the essential physics included in full-scale hydrodynamical simulations, such as (1) gravitational…

We solve the recombination equation by taking into account the induced recombinations and a physical cut off in the hydrogen spectrum. The effective recombination coefficient is parametrized as a function of temperature and free electron…