A lot of absorption lines are in the bluewards of Lyα emission line of quasar which is well-known as Lyαforest. Most of absorption lines in this forest belong to the Lyα absorption of the neutral hydrogen in the inter-galactic medium (IGM). For high redshift quasars and in the continuum with low and medium resolution, there are no many regions without absorption, so that, the quasar continuum i...

I review results obtained from studies of the high-redshift Lyα forest, and present new results from HST/STIS spectra of low-redshift quasars in comparison with cosmological hydrodynamic simulations. The evolution of the Lyα forest from z ∼ 3 → 0 is well-described by current structure formation models, in which Lyα forest absorbing gas at all red-shifts traces moderate-overdensity large-scale s...

Absorption between the rest-frame wavelengths of 973Å and 1026Å in quasar spectra arises from two sources: one is due to Lyα absorption by materials at a low redshift, and the other from Lyβ at a higher redshift. These two sources of absorption are to a good approximation uncorrelated because of their wide physical separation. Therefore, the two-point correlation of absorption in this region of...

We present predictions of the correlation between the Lyα forest absorption in quasar spectra and the mass within ∼ 5h Mpc (comoving) of the line of sight, using fully hydrodynamic and hydro-PM numerical simulations of the cold dark matter model supported by present observations. The observed correlation based on galaxies and the Lyα forest can be directly compared to our theoretical results, a...

We use a large set of cosmological smoothed particle hydrodynamics (SPH) simulations to examine the effect of mass resolution and box size on synthetic Lyα forest spectra at 2 ≤ z ≤ 5. The mass resolution requirements for the convergence of the mean Lyα flux and flux power spectrum at z = 5 are significantly stricter than at lower redshift. This is because transmission in the high redshift Lyα ...

We present a new technique for detecting structure on Mpc scales in the Lyα forest. The technique is easy to apply in practice since it does not involve absorption line fitting but is rather based on the statistics of the transmitted flux. It identifies and assesses the statistical significance of regions of overor underdense Lyα absorption and is fairly insensitive to the quality of the data. ...

We present constraints on the amplitude and shape of the matter power spectrum and the density of dark matter within the framework of a standard ΛCDM model. We use a Markov chain Monte Carlo approach to combine independent measurements of the three-dimensional weak gravitational lensing shear field by the COSMOS survey, of lowand high-resolution Lyman-α (Lyα) forest flux power spectrum by SDSS ...

Three independent observational studies have now detected a narrow (∆z ≃ 0.5) dip centred at z = 3.2 in the otherwise smooth redshift evolution of the Lyα forest effective optical depth. This feature has previously been interpreted as an indirect signature of rapid photo-heating in the IGM during the epoch of He II reionisation. We examine this interpretation using a semi-analytic model of inho...

We investigate the effect of galactic winds on the Lyα forest in cosmological simulations of structure and galaxy formation. We combine high resolution N-body simulations for the evolution of the dark matter with a semi-analytic model for the formation and evolution of galaxies which includes detailed prescriptions for the long-term evolution of galactic winds. We find that the main statistical...

Primordial baryonic matter in the vast intergalactic space may be traced with Lyα resonance absorption by neutral hydrogen and singly ionized helium. The wavelengthaveraged He ii opacity shortward of 304(1+z) Å, as measured by low-resolution UV spectroscopy, is at least 4.5 times the H i opacity shortward of 1216(1+z) Å. While a part of the He ii opacity arises from the intergalactic regions th...