SINGS Observations of Spiral Galaxies

M. Regan, M. D. Thornley, S. N. Vogel, K. Sheth, B. T. Draine, D. J. Hollenbach, M. Meyer, D. A. Dale, C. W. Engelbracht, R. C. Kennicutt, L. Armus, D. Calzetti, K. D. Gordon, G. Helou, C. Leitherer, S. Malhotra, G. H. Rieke, & M. J. Rieke 2007, in "Island Universes," Astrophysics and Space Science Proceedings, Springer, 341

One process in the secular evolution of galaxies is the formation of pseudobulges.The formation of these pseudo-bulges requires the inflow of gas to smaller radii. If the inflow rate is faster than the rate of star formation, a central concentration of gas will form. In this paper we present radial profiles of stellar and 8 micron emission from Polycyclic Aromatic Hydrocarbons (PAHs) for 11 spiral galaxiesto investigate whether the interstellar medium in these galaxies contains a centralconcentration above that expected from the exponential disk. We find that in five of the 11 galaxies there is a central excess in the 8 micron and CO emission above the inner extrapolation of an exponential disk. In particular, all four barred galaxies in the sample have strong central excesses in both 8 micron and CO emission. This correlation suggests that the excess seen in the CO profiles is, in general, not simply due to a radial increase in the CO emissivity.

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