Massive Star Formation and Dust in Collisional Ring Galaxies: From GALEX to SPITZER

We present some first results from a GALEX and Spitzer survey of a dozen collisional ring galaxies. The combination of UV and mid-IR imaging and spectroscopy will allow us to investigate the relationship between massive star formation sites, PAH molecular-band strengths, and dust heating in these mainly simultaneous starburst rings. A deep observation of the well-known Cartwheel ring galaxy has revealed a gigantic outer UV disk which extends to at least twice the radius of the outer blue star-forming ring. A lack of UV variability in the outer Cartwheel ring rules out an intermediate-mass black hole (JMBH) as the origin of the brightest of a dozen ULX source seen by Chandra in the ring.