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Kartik Sheth (California Institute of Technology / University of Maryland)
We have studied the molecular gas properties of 30 barred and 15 unbarred spirals to a) better understand the interplay between molecular gas and star formation, b) better constrain models of gas flow in bars, c) quantify the role of the bar in the re-distribution of gas, and d) test the secular evolutionary sequence predicted by models. In the central 500 pc, we find that the mean nuclear gas surface density of barred spirals (\langle\Sigmanuc\rangle=309±71 M\sun pc-2) is three times higher than that of unbarred spirals (\langle\Sigmanuc\rangle=107±29 M\sun pc-2). 9/11 bars with \Sigmanuc > 300 M\sun pc-2 are early types. We suggest that differences in \Sigmanuc explain the observed variation in the circumnuclear star formation activity in barred and unbarred spirals. Barred spirals also have a higher central concentration of gas than unbarred spirals, providing further statistical evidence of bar-induced gas transport. The central gas concentration is correlated with the bulge size but not the bar length, indicating that the ILR, bar ellipticity and circumnuclear star formation play important roles in determining the gas accumulation. We show that star formation must be taken into account if models are to reproduce the observed gas morphologies. We find that the majority of the H\alpha emission in bars is on the leading side of the dust lane, with an average linear offset of 417±57 pc near the bar ends. To explain the offset, we propose that stars may form in dust spurs, regions of high density/low shear, upstream of the dust lanes. Finally, we classify the molecular gas distributions in bars, and find that they are consistent with the predicted secular evolutionary sequence. However, the data show that not every late type bar evolves into an early type, and/or bar-induced gas inflow is periodic.
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The author(s) of this abstract have provided an email address for comments about the abstract: kartik@astro.caltech.edu