The Starburst-Driven Molecular Wind in NGC 253 and the Suppression of Star Formation

TL;DR

This study uses high-resolution observations of NGC 253 to directly measure molecular wind outflows, revealing their significant role in suppressing star formation in starburst galaxies.

Contribution

It provides the first direct measurement of molecular outflow rates at 50 pc resolution, linking molecular shells to wind suppression of star formation.

Findings

Molecular outflow rate > 3 solar masses per year

Outflow rate likely around 9 solar masses per year

Mass-outflow to star formation rate ratio of 1-3

Abstract

The under-abundance of very massive galaxies in the universe is frequently attributed to the effect of galactic winds. Although ionized galactic winds are readily observable most of the expelled mass is likely in cooler atomic and molecular phases. Expanding molecular shells observed in starburst systems such as NGC 253 and M 82 may facilitate the entrainment of molecular gas in the wind. While shell properties are well constrained, determining the amount of outflowing gas emerging from such shells and the connection between this gas and the ionized wind requires spatial resolution <100 pc coupled with sensitivity to a wide range of spatial scales, hitherto not available. Here we report observations of NGC 253, a nearby starburst galaxy (D~3.4 Mpc) known to possess a wind, which trace the cool molecular wind at 50 pc resolution. At this resolution the extraplanar molecular gas closely tracks the H{\alpha} filaments, and it appears connected to molecular expanding shells located in the starburst region. These observations allow us to directly measure the molecular outflow rate to be > 3 Msun/yr and likely ~9 Msun/yr. This implies a ratio of mass-outflow rate to star formation rate of at least {\eta}~1-3, establishing the importance of the starburst-driven wind in limiting the star formation activity and the final stellar content.