The Radial Distribution of the Interstellar Medium in Disk Galaxies: Evidence for Secular Evolution

M. W. 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, B. Buckalew, D. Calzetti, K. D. Gordon, G. Helou, C. Leitherer, S. Malhotra, E. Murphy, G. H. Rieke, M. J. Rieke, J. D. Smith 2006, ApJ, 652, 1112

One possible way for spiral galaxies to internally evolve would be for gas to flow to the center and form stars in a central disk (pseudo-bulge). 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 galaxies to investigate whether the interstellar medium in these galaxies contains a central concentration above that expected from the exponential disk. In general, we find that the two-dimensional CO and PAH emission morphologies are similar, and that they exhibit similar radial profiles. We find that in 6 of the 11 galaxies there is a central excess in the 8 \u03bcm and CO emission above the inward 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. These correlations suggest that the excess seen in the CO profiles is, in general, not simply due to a radial increase in the CO emissivity. In the inner disk, the ratio of the stellar to the 8 \u03bcm radial surface brightness is similar for 9 of the 11 galaxies, suggesting a physical connection between the average stellar surface brightness and the average gas surface brightness at a given radius. We also find that the ratio of the CO to 8 micron PAH surface brightness is consistent over the sample, implying that the 8 micron PAH surface brightness can be used as an approximate tracer of the interstellar medium.

[ADS Entry]

ADS Citation Query
# citations = 18
average # citations/year = 6.00 (# years = 3)
# citations vs. year [year=citations]
[2009=6] [2008=7] [2007=5] [2006=1]
[determined from ADS on 23 Jul 2009]