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C. Churchill (NMSU), S. Ellison (UVic), S. Rix, M. Pettini (IoA)
The goal of the Complete Optical Radio Absorption Line System (CORALS) survey is to quantify the bias introduced by dust obscuration in absorbing galaxies found in optically selected, magnitude limited QSO samples.
Biasing due to dust obscuration could significantly alter measurements of the global mass density of neutral hydrogen (HI), of the shape and evolution of the HI mass distribution function, and of the metallicity in the highest HI column density systems (i.e damped Lyman-\alpha absorbers, DLAs). These quantities are key to our understanding of the global baryon budget in highly formed structures.
CORALS I covered the redshift range z=2 to z=3. At these redshifts, we found no significant difference in the mass density of neutral gas in absorbers compared to optically selected surveys. However, since the bulk of star formation occurs by z ~1, biasing due to dust obscuration may become significant at lower redshifts. We have now undertaken CORALS II, which covers the redshift range z=0.7 to z=1.6. We have used the MgII absorption selection technique used by Rao & Turnshek (2000, ApJS, 130, 1) to find DLAs in a sample of 75 QSOs with no optical magnitude limit. We present results from the low redshift survey and discuss implications for absorption system selection and their statistics.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.