Super star clusters — extremely massive clusters found predominately in starburst environments — are essential building blocks in the formation of galaxies and thought to dominate star formation in the high-redshift universe .
However , the transformation from molecular gas into these ultra-compact star clusters is not well understood .
To study this process , we used the Submillimeter Array and the Plateau de Bure Interferometer to obtain high angular resolution ( \sim 1 \farcs 5 or 160 pc ) images of the Antennae overlap region in CO ( 2–1 ) to search for the molecular progenitors of the super star clusters .
We resolve the molecular gas distribution into a large number of clouds , extending the differential cloud mass function down to a 5 \sigma completeness limit of 3.8 \times 10 ^ { 5 } M _ { \odot } .
We identify a distinct break in the mass function around log M _ { mol } / M _ { \odot } \approx 6.5 , which separates the molecular clouds into two distinct populations .
The smaller , less massive clouds reside in more quiescent areas in the region , while the larger , more massive clouds cluster around regions of intense star formation .
A broken power-law fit to the mass function yields slopes of \alpha = -1.39 \pm 0.10 and \alpha = -1.44 \pm 0.14 for the low- and high-mass cloud population , well-matched to the mass function found for super star clusters in the Antennae galaxies .
We find large velocity gradients and velocity dispersions at the locations of intense star formation , suggestive of compressive shocks .
It is likely that these environmental factors contribute to the formation of the observed massive molecular clouds and super star clusters in the Antennae galaxies .