Molecular Gas Properties in the Central Kiloparsec of Barred and Unbarred Spirals

Abstract

We study the molecular gas properties in the central kiloparsec of 29 barred and 15 unbarred spirals from the BIMA Survey of Nearby Galaxies (SONG). We find that the mean nuclear molecular gas surface density of barred spirals (<Sigma_{nuc}>=309 +/- 71 Msun pc^{-2}) is three times higher than that of unbarred spirals (<Sigma_{nuc}>=107 +/- 29 Msun pc^{-2}). Nine out of the eleven bars with Sigma_{nuc} > 300 Msun pc^{-2} are early types. Comparison with estimates of the star formation threshold density (Sigma_{crit}) indicates that enhanced star formation in bars may be due to a larger fraction having Sigma_{nuc} > typical Sigma_{crit}. We also find that barred spirals are more centrally concentrated than unbarred spirals. The median value of the concentration parameter for barred spirals (f_{con}=Sigma_{nuc}/Sigma_{disk}=27.7) is a factor of four higher than that for the unbarred spirals (f_{con}=6.2). Finally we investigate the dependence of the central concentration on bar properties and find it may be weakly correlated with the bulge size, but is not correlated with the bar length. This suggests that inner Lindblad resonances, bar ellipticity and circumnuclear star formation play important roles in determining the gas accretion in the central kiloparsec. See http://www.astro.caltech.edu/~kartik/thesis.html for more detailed description of these thesis results. This research was made possible with funding from NSF grants AST-9981308, AST-9981289 and AST-9981546.