OH Megamasers and Galaxy Evolution

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AST 0098526Giovanelli The nuclei of many galaxies harbor highly energetic processes, which are thought to be powered ultimately by strong gravitational fields in the regions surrounding supermassive black holes. In special circumstances, gas orbiting or falling into the nuclear regions of galaxies can produce a luminous maser (a microwave laser) which is observed as a strong radio spectral line emanating from a galactic nucleus. Such "megamasers" --- so called because they are roughly a million times more luminous than typical masers associated with young stars found in the Milky Way --- are produced by excited H2O or OH molecules. OH megamasers in particular are foundonly in the nuclei of merging galaxies and are luminous enough to be observable at cosmological distances. The study proposed here aims to characterize and understand the relationship between merging galaxies and the production of OH megamasers with the ultimate goal of using OH megamasers to trace the merging history of galaxies as a function of cosmic time. The number evolution of galaxies with time is not yet known, although it is likely to be an important element in the galaxy evolution process. This study will (1) establish the space density of OH megamasers from a broad OH spectral line survey of merging galaxies at the Arecibo Observatory, (2) determine the spatial scale of OH masing in these systems from a study of line intensity variability, (3) characterize the type of host most favorable to producing an OH megamaser from optical spectroscopy at Palomar Observatory, and (4) characterize the potential use of OH megamasers as indicators of merging galaxies at high redshift. ***