We explore the effects of size of the box that we use for simulations of the intergalactic medium (IGM) at redshift two. We examine six simulations from the hydrodynamic code ENZO using the same cosmological and astrophysical input parameters and cell size, but different box size. We study the CDM distribution and many statistics of the Lyα forest absorption from the IGM. Larger boxes have fewe...

We investigate the effect of non-Gaussianity on the reconstruction of the initial mass field from the Lyα forest. We show that the transmitted flux of QSO absorption spectra are highly non-Gaussian in terms of the statistics, the kurtosis spectrum and scale-scale correlation. These non-Gaussianities can not be completely removed by the conventional algorithm of Gaussianization, and the scale-sc...

The Hubble Advanced Camera for Surveys has been used to obtain a narrow-band image of the weak emission peak seen at λ = 7205 Å in the Gunn-Peterson Lyβ absorption trough of the highest redshift quasar, SDSS J1148+5251. The emission looks perfectly point-like; there is no evidence for the intervening galaxy that we previously suggested might be contaminating the quasar spectrum. We derive a mor...

Strong observational evidence for a fluctuating ultraviolet background (UVB) has been accumulating through a number of studies of the H I and He II Lyα forest as well as accurate IGM metallicity measurements. UVB fluctuations could arise both from the inhomogeneous distribution of the ionizing sources and/or from radiative transfer (RT) through the filamentary IGM. In this study we investigate,...

In the low density intergalactic medium (IGM) that gives rise to the Lyman-α forest, gas temperature and density are tightly correlated. The velocity scale of thermal broadening and the Hubble flow across the gas Jeans scale are of similar magnitude (HλJ ∼ σth). To separate the effects of gas pressure support and thermal broadening on the Lyα forest, we compare spectra extracted from two smooth...

The intergalactic neutral hydrogen which is responsible for the Lyα forest of quasar absorption lines is a tracer of much larger amounts of ionised hydrogen. The ionised component has yet to be detected directly, but is expected to scatter CMB photons via the Sunyaev-Zel’dovich effect. We use hydrodynamic simulations of a LambdaCDM universe to create mock quasar spectra and CMB sky maps from th...

We present the highest quality Lyα forest spectra published to date. We have complete 7.9 km s −1 FWHM spectra between the Lyα and Lyβ emission lines of the bright, high redshift (V=15.9, z=3.05) QSO HS 1946+7658. The mean redshift of observed Lyα forest clouds is < z >= 2.7. The spectrum has a signal to noise ratio per pixel of 2 km s −1 that varies from 15 at 4190Å to 100 at 4925Å. The absorp...

We report on observations of redshifted He ii 303.8 Å absorption in the high-redshift QSO HE2347−4342 (z = 2.885, V = 16.1) with the Goddard High Resolution Spectrograph on board HST in its low resolution mode (4λ = 0.7 Å). With fλ = 3.6 10−15 erg cm−2 s−1 Å−1 at the expected position of He ii 304 Å absorption it is the most UV-bright high redshift QSO discovered so far. We show that the He ii ...