Star Formation Suppresion by Tidal Removal of Cold Molecular Gas from an Intermediate-Redshift Massive Post-Starburst Galaxy

TL;DR

This study reports the discovery of large molecular tidal features in a distant post-starburst galaxy, showing that galaxy mergers can directly remove cold gas and suppress star formation, offering an alternative to feedback-driven quenching mechanisms.

Contribution

It provides the first evidence that galaxy mergers can directly strip molecular gas at intermediate redshift, contributing to star formation suppression through tidal removal.

Findings

Molecular tidal features extend up to 64 kpc from the galaxy.

The tidal tails contain nearly half of the galaxy's cold molecular gas.

Galaxy mergers can directly remove molecular gas, suppressing star formation.

Abstract

Observations and simulations have demonstrated that star formation in galaxies must be actively suppressed to prevent the formation of over-massive galaxies. Galactic outflows driven by stellar feedback or supermassive black hole accretion are often invoked to regulate the amount of cold molecular gas available for future star formation, but may not be the only relevant quenching processes in all galaxies. We present the discovery of vast molecular tidal features extending up to 64 kpc outside of a massive z=0.646 post-starburst galaxy that recently concluded its primary star-forming episode. The tidal tails contain (1.2 +/- 0.1)x10^10 Msun of molecular gas, 47 +/- 5 % of the total cold gas reservoir of the system. Both the scale and magnitude of the molecular tidal features are unprecedented compared to all known nearby or high-redshift merging systems. We infer that the cold gas was stripped from the host galaxies during the merger, which is most likely responsible for triggering the initial burst phase and the subsequent suppression of star formation. While only a single example, this result shows that galaxy mergers can regulate the cold gas contents in distant galaxies by directly removing a large fraction of the molecular gas fuel, and plausibly suppress star formation directly, a qualitatively different physical mechanism than feedback-driven outflows.