The low density hydrogen and helium in the IGM probed by QSO absorption lines is sensitive to the amplitude and spectral shape of the metagalactic UV background. We use realistic H I and He II Lyα forest spectra, constructed from state-of-the-art hydrodynamical simulations of a ΛCDM Universe, to confirm the reliability of using line profile fitting techniques to infer the ratio of the metagalac...

The first galaxies formed at high redshifts, and were likely substantially less massive than typical galaxies in the local universe. We argue that (1) the reionization of a clumpy intergalactic medium (IGM) by redshift z ≈ 6, (2) its enrichment by metals by z ≈ 3 without disturbing the Lyα forest, and (3) the presence of supermassive black holes powering the recently discovered bright quasars a...

1 The shape of the UV ionizing background is reconstructed from optically thin metal absorption-line systems identified in spectra of HE 2347–4342, Q 1157+3143, and HS 1700+6416 in the redshift interval 1.8 < z < 2.9. The systems are analyzed by means of the Monte Carlo Inversion method completed with the spectral shape recovering procedure. The UVB spectral shape fluctuates at 2.4 < z < 2.9 mo...

We probe the scale dependence of the primordial spectrum in the light of the three-year WMAP (WMAP3) alone and WMAP3 in combination with the other cosmological observations such as galaxy clustering and Type Ia Supernova (SNIa). We pay particular attention to the combination with the Lyman α (Lyα) forest. Different from the first-year WMAP (WMAP1), WMAP3’s preference on the running of the scala...