UV Signposts of Resonant Dynamics in Disk Galaxies

Imaging in the restframe ultraviolet has proven to be an effective and vital means of tracing dynamical patterns of star formation in galaxies out to high redshifts. Using images from the Ultraviolet Imaging Telescope (UIT), Hubble Space Telescope (HST) and complementary groundbased telescopes, we have investigated the starburst activity and associated dynamics in nearby early-type disk galaxies. Concentrating on the starburst-ring (R)SA(r)ab galaxy M94 (NGC 4736), we find compelling evidence for bar-mediated resonances as the primary drivers of evolution at the present epoch. Similar ring-bar dynamics may prevail in the centers of early-type disk galaxies at high redshift. The gravitationally-lensed “Pretzel Galaxy” (0024+1654) at a redshift of ∼1.5 provides an important precedent in this regard. 1. UV Rings and Underlying Dynamics Inner rings and pseudo-rings are evident in 50% of all spiral galaxies and in more than 75% of early-type barred spirals (Kormendy 1979; de Vaucouleurs & Buta 1980; Buta & Combes 1996). These rings are often characterized by intense starbirth activity. UV imaging neatly isolates such rings from the older disk and bulge components. UIT images of M100 (NGC 4321), NGC 1317, and M94 (NGC 4736) provide textbook examples of the starburst ring phenomenon (see http://trifle.gsfc.nasa.gov/UIT/Astro1/Astro1 pictures.html). Senior Scientist, Raytheon STX Corporation Visiting Scientist, Harvard-Smithsonian Center for Astrophysics