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K. Sheth (UMD), M. W. Regan (DTM-CIW), M. D. Thornley (NRAO), L. Blitz, D. C.-J. Bock (UCB), A. Harris (UMD), T. T. Helfer (NRAO), S. N. Vogel (UMD), T. Wong (UCB)
We present new results from the ongoing BIMA CO (J=1-0) Survey of Nearby Galaxies (SONG). The BIMA SONG includes 44 spiral (Sa-Sd) galaxies with MB < 11, VHEL < 2000 km s-1, inclination < 70o and declination > -20o, of which more than half have already been observed with the BIMA mm-array. Galaxies for which CO emission is known to be extended are observed with a 7-field mosaic with a 3-4' FOV at 7'' angular resolution and 5 km/s spectral resolution; the remainder are a small minority and these are observed with a single central pointing (FOV~2').
In this poster, we discuss the large variations in CO morphology revealed by SONG, and compare the CO maps with optical and near-IR images. Though CO is the most widely used tracer of molecular gas, the exact value for the ratio of CO luminosity to H2 mass is controversial; another tracer of the molecular gas which can be used for comparison is dust. We derive dust extinction maps from optical-infrared color maps using a multiple-scattering radiative transfer model. In most galaxies, we find qualitative agreement between the CO emission and dust extinction distributions, indicating that CO is a reliable tracer of the dense gas distribution. Using H2 column densities inferred from the dust extinction maps, we study variations in the CO-to-H2 conversion factor within individual galaxies and between galaxies.
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The author(s) of this abstract have provided an email address for comments about the abstract: kartik@astro.umd.edu