The Intergalactic Medium at Large Redshifts

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PROPOSAL NO: AST 0206067PI: Sargent, W L WThe past few years have witnessed remarkable progress in understanding 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. Comparison of the results of high resolution spectroscopy with hydrodynamic cosmological simulations of the high redshift (z ~ 3) universe have shown that the Lyman alpha forest is the observational signature of an extended ionized gas arranged in the shape of filaments and sheets, the ''Cosmic web'', from which galaxies condense. This main reservoir of baryons has properties which can be characterized by gas dynamics (temperature, pressure, ionization state) on a small scale; on larger scales the gas follows the distribution and peculiar motions of the dark matter which dominates the mass content of the universe. Observations of Lyman alpha absorption probe the ionization history and baryon density of the universe as well as the variations in the dark matter distribution which leads to the formation of structure in the universe. The funded work will continue and extend observations and analyses in a program of quasar absorption line studies and a program to detect emission from the Lyman alpha forest clouds using the HIRES and LRIS instruments on the Keck Telescopes.