Volume 538, February 2012
|Number of page(s)||4|
|Published online||09 February 2012|
ALMA CO and VLT/SINFONI H2 observations of the Antennae overlap region: mass and energy dissipation⋆
Institut d’Astrophysique Spatiale, UMR 8617 CNRS, Université Paris-Sud
2 LERMA, UMR 8112 CNRS, École Normale Supérieure and Observatoire de Paris, Paris, France
Accepted: 28 December 2011
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-1. 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 Brγ, 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 107 M⊙ 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.
Key words: galaxies: individual: Antennae / galaxies: ISM / radio lines: ISM / infrared: ISM
© ESO, 2012
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