Jin Koda
Stony Brook University
Evolution of Giant Molecular Clouds in Galaxies
I will discuss the large-scale distribution, evolution, and dynamics of giant
molecular clouds (GMCs) in galaxies. The discussion will be based primarily
on recent CO(1-0) observations of M51 with the CARMA interferometer and
Nobeyama 45m telescope, and on the recent Galactic plane 13CO survey. In
particular, we find many GMCs both on spiral arms and in interarm regions
in M51, indicating they have a long lifetime comparable to the galactic
rotation timescale. Associations of giant molecular clouds (so-called GMAs)
are found only on spiral arms, and thus, they are likely unbound, short-lived
structures, being broken up across spiral arms. The molecular gas fraction is
high even in interarm regions; therefore, GMA destruction is not likely
caused by stellar feedback such as strong UV radiation or supernovae, since
these processes would destroy molecules as well as GMAs and GMCs. Instead, I
will discuss dynamically-driven GMC evolution, in which strong shear motions
in spiral arms cause GMA destruction and trigger GMC evolution.