Recent hydrodynamic simulations of galaxy formation reveal streams of cold (T ∼ 10 K) gas flowing into the centers of dark matter halos as massive as 10M⊙ at redshifts z ∼ 1–3. In this paper we show that if > ∼ 10% of the gravitational binding energy of the gas is radiated away, then the simulated cold flows are spatially extended Lyα sources with luminosities, Lyα line widths, and number densi...

We present the far-UV spectrum of the quasar HS 1700+6416 taken with FUSE. This QSO provides the second line of sight with the He  absorption resolved into a Lyα forest structure. Since HS 1700+6416 is slightly less redshifted (z em = 2.72) than HE 2347-4342, we only probe the post-reionization phase of He , seen in the evolution of the He  opacity, which is consistent with a simple power...

Determining when and how the first galaxies reionised the intergalactic medium promises to shed light on both the nature of the first objects and the cosmic history of baryons. Towards this goal, quasar absorption lines play a unique role by probing the properties of diffuse gas on galactic and intergalactic scales. In this review, we examine the multiple ways in which absorption lines trace th...

We measure the power spectrum, PF (k, z), of the transmitted flux in the Lyα forest using 3035 high redshift quasar spectra from the Sloan Digital Sky Survey. This sample is almost two orders of magnitude larger than any previously available data set, yielding statistical errors of ∼ 0.6% and ∼ 0.005 on, respectively, the overall amplitude and logarithmic slope of PF (k, z). This unprecedented ...

To study the nature of low z Lyα absorbers in the spectra of QSOs, we have obtained high signalto-noise UV spectra of H 1821+643 (zem = 0.297) and PG 1116+215 (zem = 0.177) with the Goddard High Resolution Spectrograph on the Hubble Space Telescope. The spectra have minimum S/N ∼ 70-100 and 3σ limiting equivalent widths of 50-75 mÅ at a resolution of ∼150 km s. Excluding lines within 3000 km s ...

Context. Charge transfer (or exchange) reactions between hydrogen atoms and protons in collisionless shocks of supernova remnants (SNRs) are a natural way of producing broad Balmer, Lyman and other lines of hydrogen. Aims. We wish to quantify the importance of shock-induced, non-thermal hydrogen emission from SNRs in young galaxies. Methods. We present a method to estimate the luminosity of bro...

We create stacked composite absorption spectra from Hubble Space Telescope Faint Object Spectrograph data from four quasi-stellar objects to search for absorption lines in the extreme ultraviolet wavelength region associated with Lyα forest absorbers in the redshift range 1.6 < z < 2.9. We successfully detect O V λ630 in Lyα absorbers throughout the 1013 to 1016.2 cm−2 column density range. For...

We simulate the Lyα forest in a standard CDM universe using a 2–level hierarchical grid code to evolve the dark and baryonic matter components self–consistently. We solve the time–dependent ionization equations for hydrogen and helium, adopting the Haardt & Madau (1996) estimate for the metagalactic UV radiation background. We compare our simulation results with the measured properties of the L...

The Lyα emitters found at z ∼ 4.5 by the Large Area Lyman Alpha (LALA) survey have high equivalent widths in the Lyα line, which can be produced by either narrow-lined active galactic nuclei (AGNs) or by stellar populations with a very high proportion of young, massive stars. To investigate the AGN scenario, we obtained two deep Chandra exposures to study the X-ray nature of the Lyα emitters. T...

There is increasingly strong evidence that gamma-ray bursts (GRBs) are associated with star-forming galaxies, and occur near or in the star-forming regions of these galaxies. These associations provide indirect evidence that at least the long GRBs detected by BeppoSAX are a result of the collapse of massive stars. The recent evidence that the light curves and the spectra of the afterglows of GR...