On the enrichment of the intergalactic medium by galactic winds

Biman Nath; Neil Trentham

doi:10.1093/mnras/291.3.505

paper

On the enrichment of the intergalactic medium by galactic winds

arXiv:astro-ph/9707177 · doi:10.1093/mnras/291.3.505

Abstract

Observations of metal lines in $\lyal$ absorption systems of small H~I column density and their ubiquitous nature suggest that the intergalactic medium (IGM) was enriched to about $Z \sim 0.01 Z_{⊙}$ by a redshift $z \sim 3$ . We investigate the role of winds from small star-forming galaxies at high $z$ in enriching the IGM. The existence of large numbers of small galaxies at high $z$ follows naturally from hierarchical clustering theories (e.g. CDM). For analytical simplicity we assume that the galactic winds escape the galaxies at a single characteristic redshift $z_{in}$ , and we model the galactic winds as spherical shock waves propagating through the IGM. We then calculate the probability distribution of the metallicity of the IGM, as a function of time (for different values of $z_{in}$ ), adopting plausible galaxy mass functions (from Press-Schechter formalism), cooling physics, star-formation efficiencies, gas ejection dynamics, and nucleosynthesis yields. We compare this expected distribution with the observed distribution of metallicities in the Ly $α$ forest at $z = 3$ , the metal poor stars in the halo of our Galaxy, and with other observational constraints on such a scenario. We find that galactic winds at high $z$ could have enriched the IGM to a mean metallicity of $Z \sim 0.01 Z_{⊙}$ at $z \sim 3$ , with a standard deviation of the same order, if $z_{in} \la 5$, and that this satisfies all the observational constraints.

Latex file with mn.sty and 6 figures. Accepted for publication in the MNRAS

On the enrichment of the intergalactic medium by galactic winds

Abstract

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