Computer Science
Scientific paper
Jul 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002hst..prop.9441k&link_type=abstract
HST Proposal ID #9441
Computer Science
Hst Proposal Id #9441
Scientific paper
The evolution of metallicity in damped Lyman alpha {DLA} quasar absorption systems is an important constraint on the global star formation history of the universe, but remains a big puzzle at present. The H I column density weighted mean metallicity in DLAs is expected to rise to solar values at low redshifts, based on cosmic chemical evolution models, because the mass-weighted mean metallicity of local galaxies is near- solar. However, current DLA abundance studies are highly uncertain and cannot distinguish between evolution and no evolution in the mean metallicity at redshifts 0.4 < z < 3.5. The existing data are particularly incomplete because no Zn measurements exist for z < 0.4, and only 2 exist for z < 0.5, which spans the past 35-45 % of the age of the universe. To pin down the cosmic age-metallicity relation all the way to the present epoch, we propose to measure Zn abundances in five DLAs at 0.1 < z < 0.5. We propose to use HST STIS because it is the only existing instrument that can measure the necessary UV lines. Our observations will clearly distinguish between no metallicity evolution vs. the predicted evolution. Our data will also provide Cr measurements, which will help to estimate the dust abundance. The proposed observations are crucial for tying together the absorption and emission histories of gas and stars in galaxies and for clarifying the relation of DLAs to present-day galaxies.
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