Star cluster survival and compressive tides in Antennae-like mergers

TL;DR

This study demonstrates that transient compressive gravitational tides during galaxy mergers can promote star cluster formation and survival, aligning with observations in the Antennae galaxies and suggesting a universal process in galaxy evolution.

Contribution

It reveals the role of transient compressive tides in star cluster formation and survival during galaxy mergers, supported by N-body simulations and observational data.

Findings

~15% of disc material experiences compressive tides at pericentre

Spatial distribution of young clusters matches simulation predictions

Characteristic time in compressive tides is ~10 Myr, similar to star formation timescales

Abstract

Gravitational tides are widely understood to strip and destroy galactic substructures. In the course of a galaxy merger, however, transient totally compressive tides may develop and prevent star forming regions from dissolving, after they condensed to form clusters of stars. We study the statistics of such compressive modes in an N-body model of the galaxy merger NGC 4038/39 (the Antennae) and show that ~15% of the disc material undergoes compressive tides at pericentre. The spatial distribution of observed young clusters in the overlap and nuclear regions of the Antennae matches surprisingly well the location of compressive tides obtained from simulation data. Furthermore, the statistics of time intervals spent by individual particles embedded in a compressive tide yields a log-normal distribution of characteristic time ~10 Myr, comparable to star cluster formation timescales. We argue that this generic process is operative in galaxy mergers at all redshifts and possibly enhances the formation of star clusters. We show with a model calculation that this process will prevent the dissolution of a star cluster during the formation phase, even for a star formation efficiency as low as ~10%. The transient nature of compressive tides implies that clusters may dissolve rapidly once the tidal field switches to the usual disruptive mode.