EAS Publications Series
Volume 24, 2007CRAL-2006. Chemodynamics: From First Stars to Local Galaxies
|Page(s)||157 - 162|
|Published online||21 April 2007|
E. Emsellem, H. Wozniak, G. Massacrier, J.-F. Gonzalez, J. Devriendt and N. Champavert (eds)
EAS Publications Series, 24 (2007) 157-162
When Does the Intergalactic Medium Become Enriched?
Steward Observatory, 933 N. Cherry Ave., Tucson, AZ, USA
We use cosmological hydrodynamic simulations including galactic feedback based on observations of local starbursts to find a self-consistent evolutionary model capable of fitting the observations of the intergalactic metallicity history as traced by C iv between z = 6.0 → 1.5. Our main finding is that despite the relative invariance in the measurement of Ω(C iv) as well as the column density and linewidth distributions over this range, continual feedback from star formation-driven winds are able to reproduce the observations, while an early enrichment scenario where a majority of the metals are injected into the IGM at z > 6 is disfavored. The constancy of the C iv observations results from a rising IGM metallicity content balanced by a declining C iv ionization fraction due to a 1) decreasing physical densities, 2) increasing ionization background strength, and 3) metals becoming more shock-heated at lower redshift. Our models predict that ~20× more metals are injected into the IGM between z = 6 → 2 than at z > 6. We show that the median C iv absorber at z = 2 traces metals injected 1 Gyr earlier indicating that the typical metals traced by C iv are neither from very early times nor from very recent feedback.
© EAS, EDP Sciences, 2007