C IV Absorption from Galaxies in the Process of Formation

Abstract

We investigate the heavy element QSO absorption systems caused by gas condensations at high redshift that evolve into galaxies at the present epoch. Artificial QSO spectra were generated for a variety of lines of sight through regions of the universe simulated with a hydrodynamics code. The C IV and H I absorption features in these spectra closely resemble observed C IV and H I absorption systems if [C/H] ~ -3 to -2 is assumed. C IV absorption complexes with multiple-component structure and velocity spreads up to ~600 km s-1 are found. The broadest systems are caused by lines of sight passing through groups of protogalactic clumps aligned along filamentary structures expanding with the Hubble flow. Typical clumps have a radius of about 5--10 kpc, a baryonic mass of ~109 Msolar, and are surrounded by hot gas atmospheres with a radius of about 30 kpc. The temperature of a considerable fraction of the gas does not take the photoionization equilibrium value. This invalidates density and size estimates derived from thermal equilibrium models. Our model may be able to explain both high-ionization multicomponent heavy-element absorbers and damped Ly alpha systems as groups of small protogalactic clumps.