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] 1 Ϫ3 to Ϫ2 is assumed. C IV absorption complexes with multiple-component structure and velocity spreads up to 1600 km s Ϫ1 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 110 9 M J , 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␣ systems as groups of small protogalactic clumps.

The physics of the intergalactic medium

“…Several observed features are reproduced by the models. The metal absorption features arise within the substructure of systems that give rise to the H I Ly-␣ features, and may result in multiple features corresponding to a single H I system ͑Haehnelt et al, 1996;Hellsten et al, 1997;Rauch, Haehnelt, and Steinmetz, 1997;Zhang et al, 1997͒. The frequencies of C II, C IV, Si IV, and N V systems are comparable to those observed at z Ӎ 3 assuming a QSO-or AGN-dominated UV background and metallicities of ͓C/H͔Ӎ−2.5 ͑Hellsten et al, 1997͒.…”

CIV absorbers inz ${>4}$ quasars: Tracing early galactic halos evolution

“…Moreover, simulations have shown that the observed CIV kinematic structure and column densities can be well reproduced by merging of proto-galactic clumps (Haehnelt et al 1996). Compact halos of hot gas with temperature close to ∼10 5 K satisfactorily explain the observed multicomponent nature of the CIV absorbers.…”

The Lyman Alpha Forest in the Spectra of Quasistellar Objects

“…As a crude general rule, the Eulerian codes are capable of higher resolution for the void regions producing the lowest column density Lyα forest, whereas the Lagrangian codes are superior for regions like minihalos or galaxies where a larger dynamic range is required. Thus the use of SPH codes has been extended to study damped Lyα systems and metal absorption systems (Haehnelt et al 1996b). Hybrid schemes (e.g.…”