Dynamical influences on star formation in spiral galaxies

The principal dynamical influences on large-scale star formation in relatively undisturbed spiral galaxies are reviewed, using recent observations on flocculent galaxies, spiral arms, bars, resonance rings, and circumnuclear starbursts. Non-axisymmetric features in the gravitational potential like bars and spiral arms impact star formation in at least two ways. They cause radial flows of gas, influencing where gas concentrates and therefore where star formation is likely. They also affect the kinematics and density of gas, and therefore its susceptibility to instabilities. The local gravitational instability theory is relatively successful in predicting whether or not gas in a given location undergoes star formation, on scales ranging from outer disks to starbursting central regions. Much about galaxy evolution depends on the relative values of the radial flow rate and the star formation rate, both of which are strongly influenced by galaxy dynamics.