Cold gas in the Milky Way's nuclear wind

TL;DR

This paper reports the first detection of cold molecular gas in the Milky Way's nuclear wind, revealing a previously unseen phase of outflow that could influence star formation and galactic evolution.

Contribution

It provides the first observational evidence of cold molecular gas in the Galactic center's outflow, expanding understanding of multiphase galactic winds.

Findings

Detection of molecular gas associated with atomic hydrogen clouds

Molecular clouds are mixing and possibly being disrupted in the outflow

The molecular outflow mass could significantly affect star formation rates

Abstract

The centre of the Milky Way is the site of several high-energy processes that have strongly impacted the inner regions of our Galaxy. Activity from the super-massive black hole, Sgr A*, and/or stellar feedback from the inner molecular ring expel matter and energy from the disc in the form of a galactic wind. Multiphase gas has been observed within this outflow, from hot highly-ionized, to warm ionized and cool atomic gas. To date, however, there has been no evidence of the cold and dense molecular phase. Here we report the first detection of molecular gas outflowing from the centre of our Galaxy. This cold material is associated with atomic hydrogen clouds travelling in the nuclear wind. The morphology and the kinematics of the molecular gas, resolved on ~1 pc scale, indicate that these clouds are mixing with the warmer medium and are possibly being disrupted. The data also suggest that the mass of molecular gas driven out is not negligible and could impact the rate of star formation in the central regions. The presence of this cold, dense, high-velocity gas is puzzling, as neither Sgr A* at its current level of activity, nor star formation in the inner Galaxy seem viable sources for this material.