Computer Science
Scientific paper
Jun 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005sptz.prop20757k&link_type=abstract
Spitzer Proposal ID #20757
Computer Science
Scientific paper
Damped Lyman-alpha absorbers (DLAs) in quasar spectra contain a large fraction of the neutral gas in galaxies and offer the most comprehensive information about chemical composition of distant galaxies. Recent observations, including our HST and MMT spectroscopy, are suggesting that the global mean metallicity of DLAs is relatively low at all redshifts, contrary to the predictions of cosmic chemical evolution models. Furthermore, imaging observations of most DLAs are suggesting star formation rates (SFRs) far below the global mean SFR. These "missing-metals" and "missing-stars" problems could be dust selection effects, since the more metal-rich and more star-forming DLAs may obscure background quasars more. As a first step toward characterizing the properties and distribution of dust in DLAs and their environments, here we propose a search for the IR emission and absorption signatures of the dust in a pilot sample of 5 DLAs at 0.3 < z < 2.8. All of these DLAs show signs of large amounts of dust, (e.g., detections of the 2175 A dust feature or H2 or large depletions). Furthermore, each field shows several spectroscopically identified galaxies with Ly-alpha, H-alpha, [O II] or [O III] emission. We propose to obtain IRAC and MIPS images to detect the dust emission from the DLAs and their companion galaxies. We also propose to obtain IRS spectra of one of the background quasars to search for the redshifted 9.7 micron silicate absorption feature in this dusty DLA. The proposed observations will constrain (a) the rest-frame IR luminosities, (b) the nature of the stellar populations, (c) the extinction curve and dust composition, and (d) the unattenuated SFRs in the DLAs and their environments. These observations will provide the first detailed IR look at DLAs, and will help to quantify the role of dust in observations of DLAs and high-z galaxies in general. Spitzer is essential because it is the only existing facility with the necessary wavelength coverage and sensitivity.
Kulkarni Varsha
Woodgate Bruce
York Donald
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