Studies of quasar absorption lines reveal that the low density intergalactic medium at z \sim 3 is enriched to 10 ^ { -3 } -10 ^ { -2 } solar metallicity .
This enrichment may have occurred in an early generation of Population III stars at redshift z \gtrsim 10 , by protogalaxies at 6 \lesssim z \lesssim 10 , or by larger galaxies at 3 \lesssim z \lesssim 6 .
This paper addresses the third possibility by calculating the enrichment of the IGM at z \gtrsim 3 by galaxies of baryonic mass \gtrsim 10 ^ { 8.5 } { M _ { \odot } } .
We use already completed cosmological simulations to which we add a prescription for chemical evolution and metal ejection by winds , assuming that the winds have properties similar to those observed in local starbursts and Lyman-break galaxies .
Results are given for a number of representative models , and we also examine the properties of the galaxies responsible for the enrichment as well as the physical effects responsible for wind escape and propagation .
We find that winds of velocity \gtrsim 200 - 300 { km s ^ { -1 } } are capable of enriching the IGM to the mean level observed , though many low-density regions would remain metal free .
Calibrated by observations of Lyman-break galaxies , our calculations suggest that most galaxies at z \gtrsim 3 should drive winds that can escape and propagate to large radii .
The primary effect limiting the enrichment of low-density IG gas 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 of redshift .