Related papers: The UV Background and the Lyman alpha Clouds at Hi…
Low mass, low metallicity galaxies at low to moderate ($z\lesssim3$) redshifts offer the best opportunity for detailed examination of the interplay between massive stars, ionizing radiation and gas in sources similar to those that likely…
The observed scatter in intergalactic Lyman-$\alpha$ opacity at $z \lesssim 6$ requires large-scale fluctuations in the neutral fraction of the intergalactic medium (IGM) after the expected end of reionization. Post-reionization models that…
Motivated by the claimed detection of a large population of faint active galactic nuclei (AGN) at high redshift, recent studies have proposed models in which AGN contribute significantly to the z > 4 H I ionizing background. In some models,…
The rapidly declining population of bright quasars at z~3 appears to make an increasingly small contribution to the ionising background at the HI Lyman limit. It is then generally though that massive stars in (pre-)galactic systems may…
Knowledge of the evolution of the low column density end of the Ly alpha forest (12.8 < log N_HI < 16.0 cm^-2) can provide substantial insight for models of structure formation and studies of the evolution of the ionizing background. Here…
We describe an ongoing experiment to search for the meta-galactic Lyman-continuum background at z~2-3. We are obtaining one of the deepest optical spectra ever, using LRIS/Keck-II to search for the fluorescent Ly-alpha emission from…
Recent observations suggest that helium became fully ionized around redshift z ~ 3. The HeII optical depth derived from the Lyman-alpha forest decreases substantially from this period to z ~ 2; moreover, it fluctuates strongly near z ~ 3…
We review the spectral properties of the population of star forming galaxies at z = 3 discovered using a colour selection technique which targets the Lyman discontinuity at 912 Angstroms. The UV luminosity of the typical z = 3 galaxy…
We revisit the proximity effect produced by QSOs at redshifts 2.1-3.3 applying the FLO approach (Saitta et al. 2008) to a sample of ~6300 Ly-alpha lines fitted in 21 high resolution, high signal-to-noise spectra. This new technique allows…
We present a semi-analytical model of star formation which explains simultaneously the observed UV luminosity function of high redshift Lyman break galaxies (LBGs) and luminosity functions of Lyman-alpha emitters. We consider both models…
Metal line ratios in a sample of 13 quasar spectra obtained with the HIRES spectrograph on the KeckI telescope have been analyzed to characterize the evolution of the metagalactic ionizing flux near a redshift of 3. The evolution of…
The recent discovery by Cowie \etal and Tytler \etal of metals in the \Lya clouds shows that the intergalactic medium (IGM) at high redshift is contaminated by the products of stars, and suggests that ionizing photons from massive star…
We present results from a new Keck spectroscopic survey of UV-faint LBGs in the redshift range 3<z<7. Combined with earlier Keck and published ESO VLT data, our sample contains more than 600 dropouts, offering new insight into the nature of…
We report new HST COS and STIS spectroscopy of a star-forming region (~100 solar masses/year) in the center of the X-ray cluster RXJ1532.9+3021 (z=0.362), to follow-up the CLASH team discovery of luminous UV filaments and knots in the…
A fraction of the extragalactic near-infrared (near-IR) background light involves redshifted photons from the ultraviolet (UV) emission from galaxies present during reionization at redshifts above 6. The absolute intensity and the…
We have obtained spectroscopic redshifts using the Keck-I telescope for a sample of 73 submillimeter (submm) galaxies for which precise positions are available. The galaxies lie at redshifts out to z=3.6, with a median redshift of 2.2. The…
Recent observations have successfully detected UV or infrared flux from galaxies at the epoch of reionization. However, the origin of their radiative properties has not been fully understood yet. Combining cosmological hydrodynamic…
The redshifted ultraviolet light from early stars at z ~ 10 contributes to the cosmic near infrared background. We present detailed calculations of its spectrum with various assumptions about metallicity and mass spectrum of early stars. We…
We present a new, on-the-fly photon flux and absorption tracer algorithm designed to directly measure the contribution of different source populations to the metagalactic UV background and to the ionisation fraction of gas in the Universe.…
We study the distribution of low-redshift Ly$\alpha$ clouds in a CDM model using numerical simulations including photoionization and cooling of the baryonic component. The ionizing background is found to be efficient enough to keep most of…