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M. W. Regan (CIW/DTM), T. T. Helfer (UAz), M. D. Thornley (NRAO), S. N. Vogel, K. Sheth, A. Harris (UMd), L. Blitz, T. Wong, D. Bock (UCB)
Even though the interstellar medium in a galaxy plays a critical role in its evolution, until now there has not been a detailed study of the distribution of the molecular gas in spiral galaxies. The BIMA Survey of CO in Nearby Spiral Galaxies (BIMA SONG) is the first systematic imaging survey of the disks of nearby spiral galaxies with sub-kiloparsec resolution. In this talk we show that the radial distribution of the CO emission in disk galaxies is substantially different from the optical or near infrared radial profiles. Our CO radial profiles contain information from both interferometer maps made with the BIMA array and from full two-dimensional single dish maps made with the NRAO 12m. The combined data allow us to be sensitive to structures on all size scales \ga 6\arcsec. The resulting radial profiles show that while in a few galaxies the CO radial profiles do seem to have an exponential structure, in most galaxies the CO profiles are far from exponential. Examples are found both where the CO emission is more centrally concentrated and less centrally concentrated than the the stellar exponential disk as traced by optical or near-infrared emission. If the CO emission is tracing the molecular gas mass, this variation in the relative central concentration is evidence that the radial distribution of molecular mass in a galaxy varies with time.