The Universe's Hydrogen Budget from z=5 to z=0: Constraints from the Lyman Alpha Forest

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Arlin Crotts 9802809 The universe's hydrogen budget from z=5 to z=0: constraints from the Lyman alpha forest Dr. Crotts is studying the connection between the Lyman alpha forest cloud sizes, shapes, clustering and number density estimates in order to compare them with those of galaxies and results from numerical models. Dr. Crotts uses numerical models that simulate the reaction of gas to collapse dominated by cold dark matter. He is using both ground based and HST data for this work. Astronomers have detailed information about the two extremes in lookback time. At zero redshift (i.e., the present) we can measure the masses of galaxies, including how much material is gaseous. At very high redshifts the isotopic abundance rations set by the Big Bang determines how much gas existed at early epochs. In between these extremes lies a complex set of conditions that are addressed by the study of the Lyman alpha forest. The Lyman alpha forest is a dense set of spectroscopic absorption lines that cluster near the Lyman alpha break in the spectrum of quasars. These lines have been identified as coming from intervening clouds between the Earth and the quasar. By mapping the distances of these clouds, one may deduce some of the large scale structure of the universe as well as other cosmological parameters. ****