Star formation in interacting galaxies

Optical spectra, Hα images and photometry, and IRAS data have been used to compare star-forming properties of otherwise similar interacting and non-interacting spiral galaxies. Star formation on all linear scales is enhanced during interactions, particularly in very close encounters. Comparison of continuum colors and Hα equivalent widths with simple models indicates that either the bursts of star formation induced by close interactions are very brief (less than 107 years) or that they are enriched in the most massive stars. These processes are minor effects on the evolution of a typical galaxy now; whether they were ever dominant depends on yet-unknown dynamical properties of binary galaxies