From large scale gas compression to cluster formation in the Antennae overlap region^⋆

Institut d’Astrophysique Spatiale, UMR 8617 CNRS, Université Paris-Sud 11, 91405 Orsay Cedex, France
e-mail: cherrera@ias.u-psud.fr

Received: 23 May 2011
Accepted: 1 September 2011

Abstract

We present a detailed observational analysis of how merger-driven turbulence may regulate the star-formation efficiency during galaxy interactions and set the initial conditions for the formation of super star clusters. Using VLT/SINFONI, we obtained near-infrared imaging spectroscopy of a small region in the Antennae overlap region, coincident with the supergiant molecular cloud 2 (SGMC 2). We find extended H₂ line emission across much of the 600 pc field-of-view, traced at sub-arcsecond spatial resolution. The data also reveal a compact H₂ source with broad lines and a dynamical mass M_dyn ~ 10⁷   M_⊙, which has no observable Brγ or K-band continuum emission, and no obvious counterpart in the 6 cm radio continuum. Line ratios indicate that the H₂ emission of both sources is powered by shocks, making these lines a quantitative tracer of the dissipation of turbulent kinetic energy. The turbulence appears to be driven by the large-scale gas dynamics, and not by feedback from star formation. We propose a scenario where the H₂ emission is related to the formation of bound clouds through accretion. The kinetic energy of the accreted gas drives the turbulence and powers the H₂ emission. Broad H₂ line widths of-order 150 km s^-1, similar to the velocity gradient of the gas across the field of view, support this idea. Within this interpretation, the compact H₂ source could be a massive cloud on its way to form a super star cluster within the next few Myr. This scenario can be further tested with ALMA observations.