Ultraviolet Imaging of NGC 3310: A Merger-driven Global Starburst

We present the first far-ultraviolet (FUV; lambda ~ 1500 A) 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 ~20% of the observed FUV flux. A linear feature (the "arrow") appears to be a star-forming tidal feature. A diffuse arc 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 Msolar yr-1 kpc-2 in the arrow to 2.1 Msolar yr-1 kpc-2 at the brightest FUV source. The striking similarity between the R1/4 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.