Ionization and Abundances of Intergalactic Gas

Abstract

We will briefly present four results — three from the W.M. Keck telescope, and one from the HST — on the abundances and ionization of the Lyman-alpha forest clouds and the intergalactic medium at high redshift. For the first time we have sufficient signal to noise to clearly see the velocity profiles of the Lyα forest lines. Most are Voigt, with little substructure, and no sign of hydrodynamics, and most have velocity dispersions between 22 and 36 km s⁻¹, below the published mean of 34 km/s. There is no correlation between velocity dispersion and column density, but some clouds are apparently very cold. We report the discovery of C IV lines in 60% of high redshift Lyα forest clouds with logN(HI) > 14.5. Ionization corrections indicate that about 50% of Lyα clouds have [C/H] > −2.5. If the few Lyα clouds with high N(HI) are the only ones with carbon, then they might all be in the very outer regions of galaxies, especially since they cluster on scales of 1000 km s⁻¹. But if all Lyα clouds have carbon, then most are intergalactic, and the carbon could have three origins: pre-galactic massive stars or very massive objects, stars inside individual intergalactic clouds, and gas ejected from galaxies. We present a low value for the primordial deuterium to hydrogen ratio in one Lyman limit absorber at high redshift, which we believe is the most accurate measurement ever, and we present an HST spectrum of the first QSO to show flux below He II 304, which means that the intergalactic medium (IGM) is highly ionized at z = 3 in this direction.