Metal absorption lines as probes of the intergalactic medium prior to the reionization epoch

Abstract

Winds from star-forming galaxies provide the most promising explanation for the enrichment of the inter-galactic medium with heavy elements. Theoretical and observational arguments indicate that the pollution may have occurred at z greater than or similar to 6; however, direct observational tests of such a scenario are needed. We model star-burst winds in the high-redshift universe and find that the fraction of space filled by enriched material varies strongly with the assumed star formation efficiency f(*) and the fraction of supernova energy powering each wind f(esc). We show that metals carried by these winds can be seen in absorption against bright background sources, such as quasars or gamma-ray bursts, in narrow lines with characteristic equivalent widths similar to0.5 Angstrom less than or similar to W less than or similar to 5 Angstrom. We argue that a substantial fraction of the metals in high-redshift winds are likely to reside in low-ionization states (C II, O I, Si II, and Fe II), but higher ionization states (C IV and Si IV) could also provide useful probes of the winds. The number of such lines can constrain both f(*) and f(esc). Statistics of metal absorption lines can also be used to identify whether H-2 is an efficient coolant in the early universe and to study the initial mass function of stars at high redshifts.