Metal Enrichment of the Intergalactic Medium atz = 3 by Galactic Winds

Studies of quasar absorption lines reveal that the low density intergalacticmedium at z ~ 3 is enriched to 0.001-0.01 solar metallicity. This enrichmentmay have occurred in an early generation of Population III stars at redshift z>~ 10, by protogalaxies at 6 <~ z <~ 10, or by larger galaxies at 3 <~ z <~ 6.This paper addresses the third possibility by calculating the enrichment of theIGM at z >~ 3 by galaxies of baryonic mass >~ 10^8.5 solar masses. We usealready completed cosmological simulations to which we add a prescription forchemical evolution and metal ejection by winds, assuming that the winds haveproperties similar to those observed in local starbursts and Lyman-breakgalaxies. Results are given for a number of representative models, and we alsoexamine the properties of the galaxies responsible for the enrichment as wellas the physical effects responsible for wind escape and propagation. We findthat winds of velocity >~ 200-300 km/s are capable of enriching the IGM to themean level observed, though many low-density regions would remain metal free.Calibrated by observations of Lyman-break galaxies, our calculations suggestthat most galaxies at z >~ 3 should drive winds that can escape and propagateto large radii. The primary effect limiting the enrichment of low-density IGgas in our scenario is then the travel time from high- to low-density regions,implying that the metallicity of low-density gas is a strong function ofredshift.Comment: 8 emulateApJ figures, 5 postscript figures. Minor revisions since last posting to match version accepted to ApJ. Major Revision since original versio