Molecular gas in the outflow of the Small Magellanic Cloud

TL;DR

This study presents the first detection of molecular gas in outflowing clouds from the Small Magellanic Cloud, revealing that star-formation-driven winds can carry cold, dense gas into the galaxy's surroundings.

Contribution

First spatially resolved detection of molecular gas in outflows from the SMC, showing cold gas can be accelerated by star-formation winds in dwarf galaxies.

Findings

Detected CO(2-1) emission in outflowing clouds

Estimated molecular gas mass of 10^3-10^4 Msun per cloud

Calculated outflow rates of 0.3-1.8 Msun/yr and high mass loading factors

Abstract

We report the first evidence of molecular gas in two atomic hydrogen (HI) clouds associated with gas outflowing from the Small Magellanic Cloud (SMC). We used the Atacama Pathfinder Experiment (APEX) to detect and spatially resolve individual clumps of CO(2-1) emission in both clouds. CO clumps are compact (~ 10 pc) and dynamically cold (linewidths < 1 km/s). Most CO emission appears to be offset from the peaks of the HI emission, some molecular gas lies in regions without a clear HI counterpart. We estimate a total molecular gas mass of 10^3-10^4 Msun in each cloud and molecular gas fractions up to 30% of the total cold gas mass (molecular + neutral). Under the assumption that this gas is escaping the galaxy, we calculated a cold gas outflow rate of 0.3-1.8 Msun/yr and mass loading factors of 3 -12 at a distance larger than 1 kpc. These results show that relatively weak star-formation-driven winds in dwarf galaxies like the SMC are able to accelerate significant amounts of cold and dense matter and inject it into the surrounding environment.