Mathematics – Logic
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997hst..prop.7475l&link_type=abstract
HST Proposal ID #7475
Mathematics
Logic
Hst Proposal Id #7475 Quasar Absorption Lines
Scientific paper
Damped Ly-alpha absorption systems provide a means of directly probing the chemical content of the universe to redshifts approaching z = 5. Previous observations have concentrated on redshifts z = 2 - 3.5, because there are very few damped Ly-alpha absorption systems known at redshifts z < 1.6. But based on an exhaustive survey at ultraviolet wavelengths, we have constructed a statistically unbiased sample of damped Ly-alpha absorption systems with neutral hydrogen column densities satisfying log N > 19.5 cmjj at redshifts z < 1.6. This sample provides the first means of systematically measuring the chemical content of the universe at redshifts z < 1.6. Here we propose an intensive investigation of moderate-redshift damped Ly-alpha absorption systems. We plan to target weak transitions of S II, Zn II, and Cr II for seven absorption systems and to obtain high- resolution WFPC2 images of the galaxies responsible for four damped Ly-alpha absorption systems. The proposed observations will provide the first chemical abundance measurements at redshifts z < 0.5, will establish the S/Si ratio as an indicator of dust content, and will probe nucleosynthetic processes by targeting undepleted elements of different nucleosynthetic origin. The proposed observations will furthermore establish the luminosities, morphological types, and impact geometries of the galaxies responsible for the absorption systems, which is essential for interpreting the abundance measurements in the context of specific galactic chemical evolution models.
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