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Intergalactic metals

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ECCA Research

Metals in the Intergalactic Medium

Spectra of high redshift QSOs reveal large numbers of intervening metal absorption lines (C, N, Si, O, etc.) in the IGM. Their origin is completely unknown. Since the only known means of forming the metals is in stars, the metal absorbers are generally believed to have originated in galaxies and subsequently been expelled into intergalactic space by winds or outflows from the galaxies (e.g., Adelberger et al 2005, ApJ, 629, 636). Little has been observationally demonstrated regarding such a scenario. It is not even known when this may have happened, or whether the metals were injected predominantly by low mass dwarf galaxies or more massive galaxies.

The metal content is also poorly constrainted. Estimates put the level of intergalactic metallicity at about 1% solar, but this uncertain by at least a factor of several because the physical state of the metal-containing gas is so uncertain due to ambiguities in the modelling of the metal absorption systems, for which generally idealised models (e.g., uniform density slabs) are adopted. An alternative approach is to predict the statistics of the distribution of metal absorption features from numerical simulations, assuming a given amount and distribution of intergalactic metals. The modelling of the metals using numerical simulations is currently being pursued at ECCA by Simon Reynolds for his PhD thesis.

Galactic winds and outflows

The introduction of metals into the IGM and subsequent mixing are not well understood either observationally or theoretically. Modelling the mixing process, necessary to interpret the metal features in individual metal absorption systems, requires both high numerical resolution galactic wind simulations (Fujita, MacLow, Ferrara & Meiksin 2004), as well as the perturbing effect of nearby galaxies, in particular during mergers. The understanding of the physical state and the origin of the metal absorption systems, and especially their relation to galaxy formation, is a long term goal at ECCA.

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