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H_2-bearing damped Lyman-alpha systems as tracers of cosmological chemical evolution

M. T. Murphy·S. J. Curran·J. K. Webb
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Abstract

The chemical abundances in damped Lyman-alpha systems (DLAs) show more than 2 orders of magnitude variation at a given epoch, possibly because DLAs arise in a wide variety of host galaxies. This could significantly bias estimates of chemical evolution. We explore the possibility that DLAs in which H_2 absorption is detected may trace cosmological chemical evolution more reliably since they may comprise a narrower set of physical conditions. The 9 known H_2 absorption systems support this hypothesis: metallicity exhibits a faster, more well-defined evolution with redshift than in the general DLA population. The dust-depletion factor and, particularly, H_2 molecular fraction also show rapid increases with decreasing redshift. We comment on possible observational selection effects which may bias this evolution. Larger samples of H_2-bearing DLAs are clearly required and may constrain evolution of the UV background and DLA galaxy host type with redshift.

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M. T. Murphy, S. J. Curran, J. K. Webb. 2003-12-09. H_2-bearing damped Lyman-alpha systems as tracers of cosmological chemical evolution. https://arxiv.org/abs/astro-ph/0310409

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