ALMA CO and VLT/SINFONI H-2 observations of the Antennae overlap region: mass and energy dissipation

We present an analysis of super-giant molecular complexes (SGMCs) in the overlap region of the Antennae galaxy merger, based on ALMA CO(3-2) interferometry and VLT/SINFONI imaging spectroscopy of H-2 1-0 S(1) at angular resolutions of 0.9 '' and 0.7 '', respectively. All but one SGMC have multiple velocity components offset from each other by up to 150 km s(-1). H-2 line emission is found in all SGMCs and the kinematics of H-2 and CO are well matched. H-2/CO line ratios vary by up to a factor of 10 among SGMCs and different velocity components of the same SGMCs. We also identify the CO counterpart of a bright, compact source of near-IR H-2 line emission, which shows no Br gamma, and was first identified with SINFONI. This source has the highest H-2/CO line ratio, and coincides with the steepest CO velocity gradient of the entire overlap region. With a size of 50 pc and a virial mass of a few 107 M-circle dot it is perhaps pre-cluster cloud that has not yet formed significant numbers of massive stars. We present observational evidence that the H-2 emission is powered by shocks, and demonstrate how the H-2 1-0 S( 1) and the CO(3-2) lines can be used as tracers of energy dissipation and gas mass, respectively. The variations in the H-2/CO line ratio may indicate that the SGMCs are dissipating their turbulent kinetic energy at different rates. The compact source could represent a short (similar to 1 Myr) evolutionary stage in the early formation of super-star clusters.