Submillimeter Array CO(2-1) Imaging of the NGC 6946 Giant Molecular
  Clouds
  We present a CO(2-1) mosaic map of the spiral galaxy NGC 6946 by combining
data from the Submillimeter Array and the IRAM 30 m telescope. We identify 390
giant molecular clouds (GMCs) from the nucleus to 4.5 kpc in the disk. GMCs in
the inner 1 kpc are generally more luminous and turbulent, some of which have
luminosities >10^6 K km/s pc^2 and velocity dispersions >10 km/s. Large-scale
bar-driven dynamics likely regulate GMC properties in the nuclear region.
Similar to the Milky Way and other disk galaxies, GMC mass function of NGC 6946
has a shallower slope (index>-2) in the inner region, and a steeper slope
(index<-2) in the outer region. This difference in mass spectra may be
indicative of different cloud formation pathways: gravitational instabilities
might play a major role in the nuclear region, while cloud coalescence might be
dominant in the outer disk. Finally, the NGC 6946 clouds are similar to those
in M33 in terms of statistical properties, but they are generally less luminous
and turbulent than the M51 clouds.
