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 Title: THE CO TRANSITION FROM DIFFUSE MOLECULAR GAS TO DENSE CLOUDS Author(s): Rice, Johnathan S Contributor(s): Federman, Steven Subject(s): Mini-symposium: ALMA's Molecular View Abstract: The atomic to molecular transitions occurring in diffuse interstellar gas surrounding molecular clouds are affected by the local physical conditions (density and temperature) and the radiation field penetrating the material. Our optical observations of CH, CH$^{+}$, and CN absorption from McDonald Observatory and the European Southern Observatory are useful tracers of this gas and provide the velocity structure needed for analyzing lower resolution ultraviolet observations of CO and H$_{2}$ absorption from Far Ultraviolet Spectroscopic Explorer. We explore the changing environment between diffuse and dense gas by using the column densities and excitation temperatures from CO and H$_{2}$ to determine the gas density. The resulting gas densities from this method are compared to densities inferred from other methods such as C$_{2}$ and CN chemistry. The densities allow us to interpret the trends from the combined set of tracers. Groupings of sight lines, such as those toward h and $chi$ Persei or Chameleon provide a chance for further characterization of the environment. The Chameleon region in particular helps illuminate CO-dark gas, which is not associated with emission from H~small{I} at 21 cm or from CO at 2.6 mm. Expanding this analysis to include emission data from the GOT C+ survey allows the further characterization of neutral diffuse gas, including CO-dark gas. Issue Date: 6/20/2017 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/96886 DOI: 10.15278/isms.2017.TF03 Date Available in IDEALS: 2017-07-272018-01-29
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