The central region of M83: massive star formation, kinematics, and the location and origin of the nucleus

Abstract

We report new near-IR integral field spectroscopy of the central starburst\nregion of the barred spiral galaxy M83 obtained with CIRPASS on Gemini-S, which\nwe analyse in conjunction with GHaFaS Fabry-Perot data, an AAT IRIS2 Ks-band\nimage, and near- and mid-IR imaging from the Hubble and Spitzer space\ntelescopes. The bulk of the current star formation activity is hidden from\noptical view by dust extinction, but is seen in the near- and mid-IR to the\nnorth of the nucleus. This region is being fed by inflow of gas through the bar\nof M83, traced by the prominent dust lane entering into the circumnuclear\nregion from the north. An analysis of stellar ages confirms that the youngest\nstars are indeed in the northwest. A gradual age gradient, with older stars\nfurther to the south, characterises the well-known star-forming arc in the\ncentral region of M83. Detailed analyses of the Pa beta ionised gas kinematics\nand near-IR imaging confirm that the kinematic centre coincides with the\nphotometric centre of M83, and that these are offset significantly, by about 3\narcsec or 60 pc, from the visible nucleus of the galaxy. We discuss two\npossible options, the first of which postulates that the kinematic and\nphotometric centre traces a galaxy nucleus hidden by a substantial amount of\ndust extinction, in the range A_V=3-10 mag. By combining this information with\nkinematic results and using arguments from the literature, we conclude that\nsuch a scenario is, however, unlikely, as is the existence of other "hidden"\nnuclei in M83. We thus concur with recent authors and favour a second option,\nin which the nucleus of the galaxy is offset from its kinematic and photometric\ncentre. This is presumably a result of some past interaction, possibly related\nto the event which lies at the origin of the disturbance of the outer disk of\nthe galaxy. (Abridged)\n