Violent quenching: molecular gas blown to 1000 km/s during a major merger

TL;DR

This study reports the discovery of a high-velocity molecular gas outflow in a galaxy merger remnant at z=0.66, driven by stellar feedback or possibly relic AGN activity, indicating a violent quenching process.

Contribution

First detailed observation of a 1000 km/s molecular outflow in a merger remnant without active AGN, highlighting a rapid quenching mechanism.

Findings

Molecular outflow velocity reaches -1000 km/s.

Outflow rate is approximately 300 solar masses per year.

The outflow is likely driven by stellar feedback, with possible relic AGN influence.

Abstract

We present Atacama Large Millimeter/submillimeter Array observations of a massive (M_stars~10^11 M_Sun) compact (r_e,UV~100 pc) merger remnant at z=0.66 that is driving a 1000 km/s outflow of cool gas, with no observational trace of an active galactic nucleus (AGN). We resolve molecular gas on scales of approximately 1-2 kpc, and our main finding is the discovery of a wing of blueshifted CO(2-1) emission out to -1000 km/s relative to the stars. We argue that this is the molecular component of a multiphase outflow, expelled from the central starburst within the past 5 Myr through stellar feedback, although we cannot rule out previous AGN activity as a launching mechanism. If the latter is true, then this is an example of a relic multiphase AGN outflow. We estimate a molecular mass outflow rate of approximately 300 M_Sun/yr, or about one third of the 10 Myr-averaged star formation rate. This system epitomizes the multiphase 'blowout' episode following a dissipational major merger - a process that has violently quenched central star formation and supermassive black hole growth.