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

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 H-2 line emission across much of the 600 pc field-of-view, traced at sub-arcsecond spatial resolution. The data also reveal a compact H-2 source with broad lines and a dynamical mass M-dyn similar to 10(7) M-circle dot, which has no observable Br gamma or K-band continuum emission, and no obvious counterpart in the 6 cm radio continuum. Line ratios indicate that the H-2 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 H-2 emission is related to the formation of bound clouds through accretion. The kinetic energy of the accreted gas drives the turbulence and powers the H-2 emission. Broad H-2 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 H-2 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.