We compare the improved measurement of the Lyα forest flux probability distribution at 1.7 < z < 3.2 presented by Kim et al. (2007) to a large set of hydrodynamical simulations of the Lyα forest with different cosmological parameters and thermal histories. The simulations are in good agreement with the observational data if the temperature-density relation for the low density intergalactic medi...

The inhomogeneous cosmological reionization process leaves tangible imprints in the intergalactic medium down to z ∼ 4− 5. The Lyman-α forest flux power spectrum provides a potentially powerful probe of the epoch of reionization. With the expected full SDSS III quasar sample (∼ 10, 000 quasars) we show that two cosmological reionization scenarios, one completing reionization at z = 6 and the ot...

Motivated by the relative lack of neutral hydrogen around Lyman Break Galaxies deduced from recent observations, we investigate the properties of the Lyα forest around high redshift galaxies. The study is based on improved numerical SPH simulations implementing, in addition to standard processes, a new scheme for multiphase and outflow physics description. Although on large scales our simulatio...

We investigate the dependence of QSO Lyα absorption features on the temperature of the absorbing gas and on the amplitude of the underlying dark matter fluctuations. We use high-resolution hydrodynamic simulations in cold dark matter dominated cosmological models. In models with a hotter intergalactic medium (IGM), the increased temperature enhances the pressure gradients between low and high d...

We investigate the hypothesis that Lyα absorption lines arise in two populations of halos — minihalos of small circular velocity (Vc < ∼ 55 km s−1) in which star formation and metal production are inhibited by photoionization of the UV background radiation, and large galactic halos (55 < ∼ Vc < ∼ 250 km s−1) which possess stars and metals. Based on the model of Lyα-absorbing gas confined in bot...

We present optical spectra of the most luminous known QSO HS 1946+7658 (zem = 3.051). Our spectra have both full wavelength coverage, 3240 – 10570 Å , and in selected regions, either high signal to noise ratio, SNR ≃ 40 – 100, or unusually high ∼ 10 km s resolution, and in parts of the Lyα forest and to the red of Lyα emission they are among the best published. We find 113 Lyα systems and six m...

Damped Lyα systems seen in the spectra of high-z QSOs arise in highdensity neutral gas in which molecular hydrogen (H2) should be conspicuous. Systematic searches to detect the H2 lines redshifted into the Lyα forest at < 3400Å are now possible thanks to the unique capabilities of UVES on the VLT. Here we summarise the present status of our on going programme to search for H2 in DLAs, discuss t...

We use an automated Voigt-profile fitting procedure to extract statistical properties of the Lyα forest in a numerical simulation of an Ω = 1, cold dark matter (CDM) universe. Our analysis method is similar to that used in most observational studies of the forest, and we compare the simulations to recently published results derived from Keck HIRES spectra. With the Voigt-profile decomposition a...

We present some statistical features of the large number of Lyα absorption lines detected in high redshift quasar spectra, obtained by using the multifractal approach. In the analysed sample of 12 QSO sight–lines, 11 show scaling behaviour with a crossover between two distinct regimes: a non-homogeneous regime at small scales and a homogeneous regime at large scales. The correlation length show...

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 CHAPTER 1: INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 CHAPTER 2: ONE-DIMENSIONAL POWER SPECTRUM . . . . . . . . . . . . 17 2.1 Three-Dimensional Power Spectrum . . . . . . . . . . . . . . . . . . . . . 17 2.2 One-Dimensional Power Spectrum . . . . . . . . . . . . . . . . . . . . . . 19 2....