Related papers: HeII Recombination Lines From the First Luminous O…
The temperature of the intergalactic medium (IGM) is set by the competition between photoheating and adiabatic cooling, which are usually assumed to define a tight equation of state in which the temperature increases monotonically with…
Star-forming galaxies are the sources likely to have reionized the universe. As we cannot observe them directly due to the opacity of the intergalactic medium at $z\gtrsim5$, we study $z\sim3\text{--}5$ galaxies as proxies to place…
The spectra of the first galaxies and quasars in the Universe should be strongly absorbed shortward of their rest-frame Lyman-alpha wavelength by neutral hydrogen (HI) in the intervening intergalactic medium. However, the Lyman-alpha line…
We interpret observations of intergalactic low ionisation metal absorption systems at redshifts z $\gtrsim$5 in terms of pressure-confined clouds. We find clouds confined by the expected pressure of galactic haloes with masses $11<\log…
We report on the detection of strongly varying intergalactic HeII absorption in HST/COS spectra of two z~3 quasars. From our homogeneous analysis of the HeII absorption in these and three archival sightlines, we find a marked increase in…
Low-ionization metal absorption lines provide a primary probe of cool gas in and around galaxies. We confront observations of metal-line absorption in quasar spectra with predictions from the IllustrisTNG cosmological simulation in order to…
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…
The temporal evolution of the ionizing UV background radiation field at high redshift provides a probe of the evolution of the early star formation rate. By comparing the observed levels of absorption in the highest redshift quasar spectra…
During the epoch of reionization a large number of photons were produced with frequencies below the hydrogen Lyman limit. After redshifting into the closest resonance, these photons underwent multiple scatterings with atoms. We examine the…
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…
Helium and hydrogen recombination lines observed in low-metallicity, extragalactic, HII regions provide the data used to infer the primordial helium mass fraction, Y_P. In deriving abundances from observations, the correction for unseen…
We investigate the role of cosmic rays from young galaxies in heating and ionizing the intergalactic medium (IGM) at high redshift. Using the IRAS observations at $60 \mu m$, we estimate the cosmic ray luminosity density at the present…
Theoretical studies and current observations of the high-redshift intergalactic medium (IGM) indicate that at least two cosmic transitions occur by the time the universe reaches gas metallicities of about $10^{-3}$ of solar values. These…
The study of high-redshift galaxies provides critical insights into the early stages of cosmic evolution, particularly during the so-called 'cosmic noon', when star formation activity reached its peak. Within this context, the origin of the…
We examine the possible reionization of the intergalactic medium (IGM) by the source UDF033238.7-274839.8 (hereafter HUDF-JD2), which was discovered in deep {\it HST}/VLT/{\it Spitzer} images obtained as part of the Great Observatory…
We present a detailed analysis of the ionization and thermal structure of the intergalactic medium (IGM) around a high-redshift QSO using a large suite of cosmological, multi-frequency radiative transfer (RT) simulations, exploring the…
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…
Ionizing sources embedded in the neutral intergalactic medium (IGM) before cosmological reionization generate discrete HII regions. We show that a sufficiently bright quasar (for example, one tenth as luminous as that recently discovered by…
The first sources of ionizing radiation to condense out of the dark and neutral IGM sent ionization fronts sweeping outward through their surroundings, overtaking other condensed objects and photoevaporating them. This feedback effect of…
IZw18 is one of the lowest-metallicity star-forming galaxies known at z$\sim$0, considered a unique local analogue of the first galaxies. The origin of its hard ionizing continuum, expected to be a common feature in the early Universe and…