ALMA CO and VLT/SINFONI H2 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 H2 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. H2 line emission
is found in all SGMCs and the kinematics of H2 and CO are well matched. H2/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 H2 line emission, which shows no Brgamma, and was
first identified with SINFONI. This source has the highest H2/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 10^7 Msun it is perhaps
a pre-cluster cloud that has not yet formed significant numbers of massive
stars. We present observational evidence that the H2 emission is powered by
shocks, and demonstrate how the H2 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 H2/CO line ratio may indicate that the SGMCs are dissipating their
turbulent kinetic energy at different rates. The compact source could represent
a short (~ 1 Myr) evolutionary stage in the early formation of super-star
clusters.
