Mathematics – Logic
Scientific paper
Mar 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008sptz.prop50783k&link_type=abstract
Spitzer Proposal ID #50783
Mathematics
Logic
Scientific paper
Understanding the nature of interstellar dust grains in distant galaxies is crucial for investigating the chemical evolution of galaxies and for correcting observations of high-redshift objects used for cosmological studies. However, very little is known about the nature of dust in the distant Universe. Absorption line systems in quasar spectra, especially the damped Lyman-alpha (DLA) absorbers, provide excellent venues for directly studying dust in distant galaxies, selected independently of the galaxy luminosities. A subset of dusty metal-rich absorption systems has been discovered using the Sloan Digital Sky Survey and radio surveys. These absorbers appear to be more massive and chemically more evolved than the general DLA population, and may contribute significantly to the global metal content. Here we propose IR spectroscopy of 10 quasars with intervening dusty DLAs to study the 9.7 micron silicate absorption feature, and in a few cases also the 18 micron silicate feature. In a recent exploratory study, we have made the first identifications of the silicate features in a few DLAs with Spitzer IRS spectra, and developed the techniques for analyzing them. Although relatively shallow, the features can be detected at a statistical level of > 10-15 sigma. The profile of the detected features resembles those seen in diffuse interstellar clouds, and in laboratory amorphous olivine. The features appear to be somewhat deeper than expected from the tau_{9.7} vs. E(B-V) relation for Galactic diffuse interstellar clouds, suggesting different dust extinction properties. We now wish to examine whether these properties are common in other DLAs and study trends with redshift, metallicity, and depletions, by studying the silicate features in other DLAs. Our sample contains both diffuse and molecular clouds spanning look-back times of 2-9 Gyr. Spitzer IRS is the only instrument available to further explore the new window on the dust in the distant Universe opened up by our exploratory study.
Kulkarni Varsha
Vladilo Giovanni
Welty Daniel E.
York Donald G.
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