The interacting dwarf galaxy NGC 3077: The interplay of atomic and molecular gas with violent star formation

We present a comprehensive multiwavelength study of the nearby interacting dwarf galaxy NGC 3077 (member of the M81 triplet). High-resolution VLA H I observations show that most of the atomic gas (similar to90%) around NGC 3077 is situated in a prominent tidal arm with a complex velocity structure. Little H I (similar to5 x 10(7) M.) is associated with NGC 3077 itself. High-resolution Owens Valley Radio Observatory (OVRO) observations of the molecular component ( CO) reveal the presence of 16 molecular complexes near the center of NGC 3077 ( total mass: similar to1.6 x 10(6) M.). A virial mass analysis of the individual complexes yields a lower CO-to-H-2 conversion factor in NGC 3077 than the Galactic value a surprising result for a dwarf galaxy. The lower conversion factor can be explained by extreme excitation conditions and the metallicity of the molecular gas. The total ( atomic and molecular) gas content in the center of NGC 3077 is displaced from the stellar component of NGC 3077 this implies that not only the gas at large galactocentric radii is affected by the interaction within the triplet but also the center. We speculate that the starburst activity of NGC 3077 was triggered by this redistribution of gas in the center: Halpha, as well as Paalpha, images show the presence of violent central star formation, as well as dramatic ionized supershells reaching galactocentric distances of similar to1 kpc. Some of these supershells are surrounded by neutral hydrogen. In a few cases, the rims of the ionized supershells are associated with dust absorption. The most prominent star-forming region in NGC 3077 as probed by Paalpha observations is hidden behind a dust cloud that is traced by the molecular complexes. Correcting for extinction we derive a star-forming rate of 0.05 M. yr(-1); i. e., given the reservoir in atomic and molecular gas in NGC 3077, star formation may proceed at a similar rate for a few times 10(8) yr. The efficiency of forming stars out of molecular gas in NGC 3077 is similar to that in M82.