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E. W. Klumpe (Department of Astronomy, University of Texas at Austin)
We have observed the 2.121 \mum (1,0)S(1) and 1.601 \mum (6,4)Q(1) lines of H2 in both the Orion A and Orion B molecular clouds. We utilized the University of Texas Near-Infrared Survey Telescope in conjunction with the University of Texas Near-Infrared Fabry-Perot Spectrometer to make the first degree-scale measurements of this extended, diffuse, emission. Our analysis of the line intensities indicates that this emission is extensive, covering the entire 8 by 8 pc region surveyed in both sources. Relative line strengths argue that, on large scales, the emission is a result of ultraviolet fluorescence and not shocks. The implications of our PDR modeling are that this fluorescent glow emanates from the surfaces of the clouds where ultraviolet photons from nearby stars impinge on the clouds and that the gas is extremely dense, on the order of 10 to 100 times denser than the average density in molecular clouds. Such high densities on the surface of the clouds imply that the morphology of the clouds is filamentary and/or sheet-like. This research was sponsored in part by the Texas Advanced Research Program under grant 003658-325 and the National Science Foundation under grant AST-9530695 to the University of Texas at Austin.