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G. R. Petitpas (University of Maryland), C. D. Wilson (McMaster University)
Near infrared galaxy surveys have revealed the existence of nuclear bars in a large number of barred or lenticular galaxies. High resolution CO maps of these galaxies exhibit a wide range of morphologies. The similarity in near infrared images combined with the wide variety of CO morphologies suggests that the molecular gas may have different properties that allow it to respond differently to similar gravitational potentials. We have performed a multi-transition CO study of the nuclei of seven double barred galaxy candidates that exhibit a variety of molecular gas morphologies in order to determine if the molecular gas properties are correlated with the nuclear structure and activity. We find that the 12CO J=3-2/J=2-1 line ratio is lower in galaxies with molecular bars in the nucleus and higher in galaxies with CO emission dispersed around the galactic center in rings and peaks. The 13CO/12CO J=2-1 line ratios are similar for all galaxies, which indicates that the J=3-2/J=2-1 line ratio is tracing variations in gas temperature and density, rather than variation in optical depth. The molecular gas in galaxies with nuclear molecular bars is cooler which may enhance the gas's ability to clump together and flow inwards. The molecular gas conditions, combined with the star formation activity and models of double barred galaxies suggest that the variation in molecular gas distributions and physical conditions may be the result of galaxy evolution though the double barred phase.
The author(s) of this abstract have provided an email address for comments about the abstract: petitpas@astro.umd.edu