Metal Enrichment of the Intergalactic Medium at z=3 by Galactic Winds

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  • 24 June 2000
Abstract
Studies of quasar absorption lines reveal that the low density intergalactic medium at z ~ 3 is enriched to 0.001-0.01 solar metallicity. This enrichment may 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 possiblity by calculating the enrichment of the IGM at z >~3 by galaxies of baryon mass >~ 10^8.5 solar masses. 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. We find that winds of velocity >~ 200-300 km/s are capable of enriching the IGM to the mean level observed, but may have trouble reproducing the observed uniformity of enrichment without excessive heating of the IGM, especially if the enrichment exists in even underdense regions of the IGM. Conversely, we argue that pollution at higher-z can provide more uniform enrichment but may have difficulty achieving a high enough mean enrichment.

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