Spatially Resolved Kinematics of the Central Regions of M83: Hidden Mass Signatures and the Role of Supernovae

Abstract

The barred grand-design spiral M83 (NGC 5236) is one of the most studied galaxies given its proximity, orientation, and particular complexity. Nonetheless, many aspects of the central regions remain controversial, conveying our limited understanding of the inner gas and stellar kinematics, and ultimately of the nucleus evolution. In this work, we present AO VLT-SINFONI data of its central ~235 × 140 pc with an unprecedented spatial resolution of ~0.2 arcsec, corresponding to ~4 pc. We have focused our study on the distribution and kinematics of the stars and the ionized and molecular gas by studying the Paα and Brγ emission in detail, the H₂ 1-0S(1) line at 2.122 μm, and the [Fe II] line at 1.644 μm, together with the CO absorption bands at 2.293 μm and 2.323 μm. Our results reveal a complex situation where the gas and stellar kinematics are totally unrelated. Supernova explosions play an important role in shaping the gas kinematics, dominated by shocks and inflows at scales of tens of parsecs that make them unsuitable to derive general dynamical properties. We propose that the location of the nucleus of M83 is unlikely to be related to the off-center "optical nucleus." The study of the stellar kinematics reveals that the optical nucleus is a gravitationally bound massive star cluster with M _dyn = (1.1 ± 0.4) × 10⁷ M _⊙, formed by a past starburst. The kinematic and photometric analysis of the cluster yield that the stellar content of the cluster is well described by an intermediate age population of log T(yr) = 8.0 ± 0.4, with a mass of M ^sstarf ~= (7.8 ± 2.4) × 10⁶ M _⊙.