Double nucleus in M83

Abstract

M 83 is one of the nearest galaxies with an enhanced nuclear star formation and it presents one of the best opportunities to study the kinematics and physical properties of a circumnuclear starburst. Our three-dimensional spectroscopy data in R band confirm the presence of a secondary nucleus or mass concentration (previously suggested by Thatte and coworkers). We determine the position of this hidden nucleus, which would be more massive than the visible one, and was not detected in the optical HST images due, probably, to the strong dust extinction. The optical nucleus has a mass of 5 x 10^6 M_Sun / sin i (r < 1&#39;&#39;.5), and the hidden nucleus, located 3&#39;&#39;.9 +/- 0&#39;&#39;.5 at the NW (PA 271 +/- 15 deg) of the optical nucleus, would have a mass of 1 x 10^7 M_Sun / sin i (r < 1&#39;&#39;.5). The emission line ratio map also unveils the presence of a second circumnuclear ring structure, previously discovered by IR imaging (Elmegreen and coworkers). The data allow us to resolve the behavior of the interstellar medium inside the circumnuclear ring and around the binary mass concentration.