Double Nucleus in M83

M 83 is one of the nearest galaxies with an enhanced nuclear star formationand it presents one of the best opportunities to study the kinematics andphysical properties of a circumnuclear starburst. Our three-dimensionalspectroscopy data in R band confirm the presence of a secondary nucleus or massconcentration (previously suggested by Thatte and coworkers). We determine theposition of this hidden nucleus, which would be more massive than the visibleone, and was not detected in the optical HST images due, probably, to thestrong dust extinction. The optical nucleus has a mass of 5 x 10^6 M_Sun / sini (r < 1''.5), and the hidden nucleus, located 3''.9 +/- 0''.5 at the NW (PA271 +/- 15 deg) of the optical nucleus, would have a mass of 1 x 10^7 M_Sun /sin i (r < 1''.5). The emission line ratio map also unveils the presence of asecond circumnuclear ring structure, previously discovered by IR imaging(Elmegreen and coworkers). The data allow us to resolve the behavior of theinterstellar medium inside the circumnuclear ring and around the binary massconcentration.Comment: 28 pages, 11 figures. Discussion updated. Published versio