Heavy Element Abundances at High Redshifts

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AST-0606868SargentThe past few years have witnessed remarkable progress in our understanding of the origin and properties of the intergalactic medium, which gives rise to the absorption features known as the "Lyman-alpha forest", in the spectra of distant quasars. Studies have shown that the Lyman-alpha forest is the observational signature of an extended ionized gas arranged in the shape of filaments and sheets, known as the cosmic web, from which galaxies condense. Thus, observations of Lyman-alpha absorption probe not only the ionization history and baryon density of the Universe, but also the dark matter variations that lead to the formation of structure. This project will a) determine the intensity and source of the radiation responsible for ionizing the intergalactic gas, b) use high resolution spectra to investigate inter-galactic clouds at the end of the reionization era, c) find more of a special class of absorbers produced in galactic outflows, and d) determine the heavy element composition of the most tenuous regions of intergalactic space. The work unites observations of the large-scale distribution of matter with numerical simulations carried out by theorists. There is sufficient large telescope access to obtain those data not already in hand.This Principal Investigator collaborates with scientists in Great Britain, Japan, Holland and Australia, and his collected data are used by colleagues across the US as well as in Poland, Russia, Holland and Great Britain. These data are also used in other fields of science, notably to investigate the composition of the earth's atmosphere and its seasonal and long-term changes. This work thus has a widespread impact in addition to its influence through publications and the associated student training.