We combine COBE-DMR measurements of cosmic microwave background (CMB) anisotropy with a recent measurement of the mass power spectrum at redshift z = 2.5 from Lyα forest data to derive constraints on cosmological parameters and test the inflationary cold dark matter (CDM) scenario of structure formation. By treating the inflationary spectral index n as a free parameter, we are able to find succ...

We present an analysis of the non-Gaussianity in the distribution of Lyα forest lines in the QSO absorption spectra. Statistical tests performed on this data indicate that there may be large scale structure even though the power spectrum of the Lyα line distribution on large scales is found to be flat. It is apparent that higher (than two) order statistics are crucial in quantifying the cluster...

We develop a method to extract the “effective equation of state” of the intergalactic medium from the Doppler (b) parameter distribution of the low-density Lyα forest. We test the method on numerical simulations and then apply it to published observations of the Lyα forest at redshifts z ≃ 0 to 4. We find that the effective equation of state is close to isothermal at redshift z ∼ 3, indicating ...

Here we describe results of our attempt to determine what types of galaxies are responsible for the Lyα forest absorption systems, based on our ongoing imaging and spectroscopic survey of faint galaxies in fields of HST spectroscopic target QSOs. Our primary conclusions are that the bulk of the Lyα forest arises in more or less normal galaxies (that span the normal range of luminosity and morph...

The spatial distribution of Lyα forest absorption systems toward a group of 8, closely spaced QSOs has been analysed and evidence for large scale structure has been found at z = 2.8. Our technique is based on the first and second moments of the transmission probability density function which is capable of identifying and assessing the significance of regions of over-or underdense Lyα absorption...

We have measured the transmission of the Lyα forest produced by neutral hydrogen scattering in the intergalactic medium between redshifts 2 and 6.3 using high signal to noise, high resolution (R ≥ 5000) observations of 50 quasars spread over the redshift range. We use a uniform set of 15Å intervals covering Lyα, Lyβ, and Lyγ absorption regions to tabulate the forest transmission as a function o...

Lyα absorber correlations contain information about the underlying density distribution associated with a particular class of absorbers. As such, they provide an opportunity to independently measure the “bias” of the Lyman alpha forest, i.e. the relationship between H I column density and underlying dark matter density. In these proceedings we use hydrodynamic simulations to investigate whether...

We use a cosmological hydrodynamic simulation of a cold dark matter universe to investigate theoretically the relationship between high redshift galaxies and the Lyα forest at redshift z = 3. Galaxies in the simulation are surrounded by halos of hot gas, which nevertheless contain enough neutral hydrogen to cause a Lyα flux decrement, its strength increasing with galaxy mass. A comparison with ...

We report a scaling of the mean matter density with the width of the saturated Lyα absorptions. This property is established using the “pseudo-hydro” technique (Croft et al. 1998). It provides a constraint for the inversion of the Lyα forest, which encounters difficulty in the saturated region. With a Gaussian density profile and the scaling relation, a simple inversion of the simulated Lyα for...

A convincing physical picture for the Lyα forest has emerged from simulations and related semi-analytic studies of structure formation models. Observations can be be used in the context of this picture to study cosmology using the structure of the forest. With the availability of well motivated predictions, not only has it become possible to test models directly, but the physical processes invo...