The formation of young massive clusters triggered by cloud-cloud collisions in the Antennae Galaxies NGC 4038/NGC 4039

TL;DR

This study provides observational evidence that cloud-cloud collisions in the Antennae Galaxies trigger the rapid formation of super star clusters, with a positive correlation between collision-induced pressure and cluster mass.

Contribution

It identifies specific signatures of cloud-cloud collisions in the Antennae Galaxies and links collision pressure to the mass of resulting super star clusters, advancing understanding of cluster formation mechanisms.

Findings

Detection of velocity-separated gas components indicating collisions.

Identification of bridge features connecting colliding clouds.

Correlation between collision pressure and super star cluster mass.

Abstract

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.