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Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997hst..prop.7451s&link_type=abstract
HST Proposal ID #7451
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Hst Proposal Id #7451 Quasar Absorption Lines
Scientific paper
Damped Ly-Alpha {DLAs} are thought to arise in the disk of the progenitors of present-day spiral galaxies. Recent surveys reveal that they contain a large fraction of the HI at high redshift, in quantities similar to the one needed to form the entire star population in the local Universe; thus the redshift evolution of the HI content of the Universe may provide clues to the evolution of the overall star formation rate. However, we recently found indications that existing surveys for z< 1 DLAs may be affected by the magnification bias due to gravitational lensing {Smette, Claeskens & Surdej 1997}. On the other hand, HST images of QSOs with 0.4 < z < 1 DLAs were studied by Le Brun et al. {1996}: several of them lie at impact parameter similar to the Einstein radius of the absorber, as derived from its luminosity. We thus expect that some of these QSOs be multiply imaged by their absorbers, but with a secondary image possibly severely absorbed by dust located in the galaxy. We suggest a search for possible secondary images due to gravitational lensing by the galaxy responsible of the absorption; we therefore propose to obtain IR images with NICMOS of 13 quasars in the spectrum of which DLAs, 21 cm or strong MgII absorption lines have been detected. As multiple images offer a direct mean of measuring the mass of the lens, HST would thus directly determine the mass associated with DLA absorbers and test the dark matter hypothesis for spiral galaxies in a way which do not rely on their dynamical properties.
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