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P.C. Guo, J. Ge, D.B. Nestor (UF), J. Prochaska (Lick), J.F. Wang (PennState)
We report detection of five strong 2175Ådust absorption systems at zabs = 0.9-1.6 among ~40,000 quasar spectra with zem>0.9 in the SDSS DR1-4. All of these absorption systems have the Milky Way type extinction with strong 2175Åabsorption bumps with high measured extinction, E(B-V)\geq 0.1. These systems along with the three previously identified systems (Wang et al. 2004) have red spectral slopes and red color (g-i>0.4), indicating dust in these absorbers are primarily responsible for the quasar spectral reddening. The total estimated neutral hydrogen density is high, N(H)>~1021cm-2. Hence, these systems represent a subgroup of Damped Lyman alpha absorbers. The Keck ESI spectroscopy of some systems shows that they have Milky Way type metallicity and dust depletion pattern, indicating these absorption systems may be associated with Milky Way type galaxies at high redshifts. Previous experiments show that the carbon-rich organic molecules might be responsible for the 2175Åabsorption. The combination of high metalicity, dust content and organic materials, the critical components for forming planets and life on Earth, in these 2175Åabsorbers suggests that planets and life might form ~10 billion years ago in the universe.
We acknowledge the support from NSF AST-0451407 and AST-0451408, NASANNG05G321G and NNG05GR41G, and the University of Florida.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.