We present moderate resolution data for 39 quasi-stellar objects (QSOs) at z ≈ 2 obtained at the Multiple Mirror Telescope. These data are combined with spectra of comparable resolution of 60 QSOs with redshifts greater than 1.7 found in the literature to investigate the distribution of Lyα forest lines in redshift and equivalent width. We find a value for γ, the parameter describing the number...

We study the spatial fluctuations in the hydrogen ionizing background in the epoch following reionization (z ∼ 5–6). The rapid decrease with redshift in the photon mean free path (m.f.p.), combined with the clustering of increasingly rare ionizing sources, can result in a very inhomogenous ionizing background during this epoch. We systematically investigate the probability density functions (PD...

We use an Eulerian hydrodynamic cosmological simulation to model the Lyα forest in a spatially flat, COBE normalized, cold dark matter model with Ω = 0.4, and find that the intergalactic, photoionized gas is predicted to collapse into sheet-like and filamentary structures which give rise to absorption lines having similar characteristics as the observed Lyα forest. A typical filament is ∼ 1hMpc...

We investigate the large-scale inhomogeneities of the hydrogen ionizing radiation field in the Universe at redshift z = 3. Using a raytracing algorithm, we simulate a model in which quasars are the dominant sources of radiation. We make use of large scale N-body simulations of a ΛCDM universe, and include such effects as finite quasar lifetimes and output on the lightcone, which affects the sha...

Using cosmological hydrodynamic simulations we measure the mean transmitted flux in the Lyα forest for quasar sightlines that pass near a foreground quasar. We find that the trend of absorption with pixel-quasar separation distance can be fitted using a simple power law form including the usual correlation function parameters r0 and γ so that (〈F (r)〉 = ∑ exp(−τeff(1 + ( r r0 )))). From the sim...

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 estimate the value of the matter density parameter Ω0 by combining constraints from the galaxy cluster mass function with Croft et al.’s recent measurement of the mass power spectrum, P (k), from Lyα forest data. The key assumption of the method is that cosmic structure formed by gravitational instability from Gaussian primordial fluctuations. For a specified value of Ω0, matching the observ...

We directly measure the evolution of the intergalactic Lyman-α effective optical depth, τeff , over the redshift range 2 ≤ z ≤ 4.2 from a sample of 84 high-resolution, high-signal-to-noise quasar spectra obtained with the ESI and HIRES spectrographs on Keck, and with the MIKE spectrograph on Magellan. This represents an improvement over previous analyses of the Lyα forest from highresolution sp...

We explore several physical effects on the power spectrum of the Lyα forest transmitted flux. The effects we investigate here are usually not part of hydrodynamic simulations and so need to be estimated separately. The most important effect is that of high column density absorbers with damping wings, which add power on large scales. We compute their effect using the observational constraints on...

We report on observations of redshifted He ii 303.8 ˚ A absorption in the high-redshift QSO HE 2347−4342 (z = 2.885, V = 16.1) with the Goddard High Resolution Spectrograph on board HST in its low resolution mode (△λ = 0.7 ˚ A). With f λ = 3.6 10 −15 erg cm −2 s −1Å −1 at the expected position of He ii 304Å absorption it is the most UV-bright high redshift QSO discovered so far. We show that th...