Metal enrichment of the intergalactic medium at z=3 by galactic winds

Studies of quasar absorption lines reveal that the low-density intergalacti c medium (IGM) at z similar to3 is enriched to between 10(-3) and 10(-2) so lar metallicity. This enrichment may have occurred in an early generation o f Population III stars at redshift z greater than or similar to 10, by prot ogalaxies at 6 less than or similar to z less than or similar to 10, or by larger galaxies at 3 less than or similar to z less than or similar to 6. T his paper addresses the third possibility by calculating the enrichment of the IGM at z greater than or similar to 3 by galaxies of baryonic mass grea ter than or similar to 10(8.5) M-circle dot. We use already completed cosmo logical simulations, to which we add a prescription for chemical evolution and metal ejection by winds, assuming that the winds have properties simila r to those observed in local starbursts and Lyman break galaxies. Results a re given for a number of representative models, and we also examine the pro perties of the galaxies responsible for the enrichment as well as the physi cal effects responsible for wind escape and propagation. We find that winds of velocity greater than or similar to 200-300 km s(-1) are capable of enr iching the IGM to the mean level observed, although many low-density region s would remain metal free. Calibrated by observations of Lyman break galaxi es, our calculations suggest that most galaxies at z greater than or simila r to 3 should drive winds that can escape and propagate to large radii. The primary effect limiting the enrichment of low-density intergalactic gas in our scenario is then the travel time from high-to low-density regions, imp lying that the metallicity of low-density gas is a strong function of redsh ift.