Ultraviolet imaging of NGC 3310: A merger-driven global starburst

We present the first far-ultraviolet (FUV; lambda similar to 1500 Angstrom) image of the nearby peculiar SAB(r)bc galaxy NGC 3310. The small 15 '' (945 pc) diameter circumnuclear starburst ring is the most luminous structure, producing 30% of the total observed FUV luminosity. Diffuse emission from the inner disk (20 '' <R <40 '') contributes another similar to 20% of the observed FUV flux. A linear feature (the ''arrow'') appears to be a star-forming tidal feature. A diffuse are observed at optical wavelengths (the ''bow'') is not visible in the FUV and is probably a tidally induced shell composed of older stars. Mean star formation rates range from 0.031 M. yr(-1) kpc(-2) in the arrow to 2.1 M. yr(-1) kpc(-2) at the brightest FUV source. The striking similarity between the R(1/4) law behavior of the FUV and B-band surface brightness profiles, combined with the very blue colors of NGC 3310, strongly argues that the present morphology is the result of a global starburst triggered by a merger with a dwarf companion.