The correlation between Lyα absorption in the spectra of quasar pairs can be used to measure the transverse distance scale at z ∼ 2, which is sensitive to the cosmological constant (ΩΛ) or other forms of vacuum energy. Using Hydro-PM simulations, I compute the three-dimensional power spectrum of the Lyα forest flux, PF (k), from which the redshift-space anisotropy of the correlation can be obta...

If an additional large scale hydrodynamic velocity field is superposed on the general Hubble flow, the peculiar velocities have the effect that spatially separated volume elements along a given line of sight may contribute to the absorption at the same value of λ. This effect leads to a ‘line-like’ absorption structure rather than to a smooth GP-depression. From this it follows that at least pa...

We have performed a detailed statistical study of the evolution of structure in a photoionized intergalactic medium (IGM) using analytical simulations to extend the calculation into the mildly non-linear density regime found to prevail at z = 3. Our work is based on a simple fundamental conjecture: that the probability distribution function of the density of baryonic diffuse matter in the unive...

The Lyα forest at z & 5.5 shows strong scatter in the mean transmission even when smoothed over very large spatial scales, & 50 Mpc/h. This has been interpreted as a signature of strongly fluctuating radiation fields, or patchy reionization. To test this claim, we calculate the scatter arising solely from density fluctuations, with a uniform ionizing background, using analytic arguments and sim...

In recent years, the possibility of measuring the cosmological constant ΩΛ through the application of the Alcock-Paczynski test to the Lyman Alpha (Lyα) forest has been suggested (McDonald et al. 1999; Hui et al. 1999). Despite the theoretical uncertainties due to a few other cosmological parameters, some of the greatest difficulties we encounter concern the huge uncertainties due to cosmic var...

We present the first results of a survey designed to understand the origin of the Lyα-forest absorption system at low redshift. Using the WYFFOS and HYDRA multifibre spectrographs on the WHT and WIYN telescopes, we have identified 51 galaxies brighter than bj = 18.5 within 30 arcmins of the sightline of the QSO 1821+643. This line of sight is of particular interest due to the detection of a pop...

The UV radiation from a quasar leaves a characteristic pattern in the distribution of ionized hydrogenthroughout the surrounding space. This pattern or light echo propagates through the intergalacticmedium at the speed of light, and can be observed by its imprint on the Lyα forest spectra of background sources. As the echo persists after the quasar has switched off, it offers the possib...

We investigate the metal species associated with Ly$\alpha$ forest in eBOSS quasar spectra. Metal absorption lines are revealed stacked spectra from cross-correlating selected absorbers and flux fluctuation field. Up to 13 identified relatively strong (those $-1.0<\delta_{\rm Ly\alpha}<-0.6$ neutral hydrogen column density of ~ $10^{15-16}$ $\rm cm^{-2}$) over absorber redshift range $2<z_{\rm ...

The recent measurement by WMAP of a large electron scattering optical depth τe = 0.17 ± 0.04 is consistent with a simple model of reionization in which the intergalactic medium (IGM) is ionized at redshift z ∼ 15, and remains highly ionized thereafter. Here, we show that existing measurements of the IGM temperature from the Lyman-alpha (Lyα) forest at z ∼ 2 − 4 rule out this “vanilla” model. Un...