The formation of young massive clusters triggered by cloud-cloud
  collisions in the Antennae Galaxies NGC 4038/NGC 4039
  The formation mechanism of super star clusters (SSCs), a present-day analog
of the ancient globulars, still remains elusive. The major merger, the Antennae
galaxies is forming SSCs and is one of the primary targets to test the cluster
formation mechanism. We reanalyzed the archival ALMA CO data of the Antennae
and found three typical observational signatures of a cloud-cloud collision
toward SSC B1 and other SSCs in the overlap region; i. two velocity components
with $\sim$100 km s$^{-1}$ velocity separation, ii. the bridge features
connecting the two components, and iii. the complementary spatial distribution
between them, lending support for collisions of the two components as a cluster
formation mechanism. We present a scenario that the two clouds with 100 km
s$^{-1}$ velocity separation collided, and SSCs having $\sim$10$^6$-10$^7$
$M_{\rm \odot}$ were formed rapidly during the time scale. {We compared the
present results with the recent studies of star forming regions in the Milky
Way and the LMC, where the SSCs having $\sim$10$^4$-10$^5$ $M_{\rm \odot}$ are
located. As a result, we found that there is a positive correlation between the
compressed gas pressure generated by collisions and the total stellar mass of
SSC, suggesting that the pressure may be a key parameter in the SSC formation.
