Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-10-15
Astronomy and Astrophysics
Astrophysics
6 pages, 1 figure, 1 table, v2: updated references, corrected typos, to appear in Recycling intergalactic and interstellar mat
Scientific paper
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.
Curran Stephen J.
Murphy Michael T.
Webb John K.
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