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 M_B < 11, VHEL < 2000 km s(-1) , inclination < 70(o) and declination > -20(o) , 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 H_2 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 H_2 column densities inferred from the dust extinction maps, we study variations in the CO-to-H_2 conversion factor within individual galaxies and between galaxies.
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1998