"Dynamical Processes in the Formation of Giant Molecular Clouds"

In our own Milky Way and other contemporary spiral galaxies, star formation takes place in giant clouds of molecular gas. Both observations and theory suggest that these clouds form and disperse rapidly, but the dynamical mechanisms involved are only incompletely understood. Focusing on the issue of cloud formation, I will introduce the various dynamical effects involved -- including gravity, large-scale shear, Coriolis forces, and magnetic stresses -- and the modes of condensation that have been proposed. I will then present results from numerical simulations that have identified the chief cloud-forming mechanisms, and along the way have explained fascinating spur-like structures recently observed in high-resolution HST images of spiral galaxies.