THE NUCLEAR STARBURST ACTIVITY IN M83 - IMAGING AT NEAR-IR WAVELENGTHS

Three colour near-IR images of the starburst nucleus of the barred galaxy NGC 5236 (M83) are presented. A sub arcsec angular resolution is achieved which leads to an improved understanding of the structure of the region. The conventional nucleus is clearly localized, and is shown to be also a star forming site. The identification of radio/10-mu-m sources NW from the nucleus allows a new positioning of the most active region of star formation which does not appear to be directly connected to the nucleus. Because of their visible and near-IR counterparts, and of their IR colours, these active star forming regions are very likely located on the edge of the molecular complex. An arc of emission SW of the nucleus is well delineated, consisting in an extended emission on which are superimposed several hot-spots: it likely corresponds to the part of a circumnuclear molecular ring where a burst of star formation is ongoing; the ring appears to be confined in the inner Linblad resonance. The evolution of near-IR colours along this arc suggests and is consistent with a mechanism of chain reaction for the stellar formation. The hot-spots along the arc have a comparable surface density to galactic star forming sites. We finally discuss the nature of a thin bridge of emission which links the nucleus to the near-IR arc and can possibly trace a flow of fresh matter from the ring to the nucleus, along a gaseous bar, a recently proposed mechanism.