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D. S. Meier, J. L. Turner (UCLA)
Results of a high spatial resolution (~4'') survey of molecular lines in the nearby starburst galaxy, IC 342, made with the Owens Valley Millimeter Interferometer are presented. Observations of 12CO, 13CO, C18O, HNC, HC3N, HNCO, C2H, SO along with existing observations of HCN, HCO+, and NH3 are discussed. Chemistry is important for governing the physical conditions of molecular gas since it can influence the cooling rate and the degree of ionization of molecular clouds in star forming regions. Maps of the CO isotopomers are used to accurately map out the distribution of H2. Column densities of other trace species are compared with H2 to derive relative abundances. Abundances of C2H, HC3N and HNCO in IC 342 are similar to those found in the Galactic Center HII region, SgrB2. However order of magnitude variations in the relative abundances of these species exist. C2H is confined to the central photodissociation region near the starburst. By contrast, HCN, HNC and HCO+ arise predominantly from the dense molecular clouds. HC3N is only seen in the dense molecular clouds that have substantial star formation associated with them. Maps of HNCO in two additional barred galaxies, Maffei 2 and NGC 6946, are displayed. In all three galaxies, the HNCO is inexplicably found to have quite high abundances away from the central starburst site or the column density peaks. HNCO peaks at the ends of the bar and at possible x1-x2 orbit intersections, consistent with sites of large scale cloud-cloud collisions. This, along with other pieces of evidence indicate the possibility that HNCO may be useful as a bright shock tracer in external galaxies. Funding for this research is provided by NSF grant AST-0071276.