Metal Enrichment of the Intergalactic Medium in Cosmological Simulations

Observations have established that the diffuse intergalactic medium (IGM) atz ~ 3 is enriched to ~0.1-1% solar metallicity and that the hot gas in largeclusters of galaxies (ICM) is enriched to 1/3-1/2 solar metallicity at z=0.Metals in the IGM may have been removed from galaxies (in which they presumablyform) during dynamical encounters between galaxies, by ram-pressure stripping,by supernova-driven winds, or as radiation-pressure driven dust efflux. Thisstudy develops a method of investigating the chemical enrichment of the IGM andof galaxies, using already completed cosmological simulations. To thesesimulations, we add dust and (gaseous) metals, distributing the dust and metalsin the gas according to three simple parameterized prescriptions, one for eachenrichment mechanism. These prescriptions are formulated to capture the basicejection physics, and calibrated when possible with empirical data. Our resultsindicate that dynamical removal of metals from >~ 3*10^8 solar mass galaxiescannot account for the observed metallicity of low-column density Ly-alphaabsorbers, and that dynamical removal from >~ 3*10^10 solar mass galaxiescannot account for the ICM metallicities. Dynamical removal also fails toproduce a strong enough mass-metallicity relation in galaxies. In contrast,either wind or radiation-pressure ejection of metals from relatively largegalaxies can plausibly account for all three sets of observations (though it isunclear whether metals can be distributed uniformly enough in the low-densityregions without overly disturbing the IGM, and whether clusters can be enrichedquite as much as observed). We investigate in detail how our results changewith variations in our assumed parameters, and how results for the differentejection processes compare. (Abridged)Comment: Minor revision, 1 figure added addressing diffusion of metals after their ejection. Accepted by ApJ. 31 EmulateApj Pages with 13 embedded postscript figure