ALMA CO(3-2) Observations of Star-Forming Filaments in a Gas-Poor Dwarf Spheroidal Galaxy

TL;DR

This study uses ALMA to observe molecular gas in a gas-poor dwarf galaxy, revealing dense clouds in filaments and their relation to star formation, with implications for understanding starburst activity in such environments.

Contribution

First high-resolution ALMA observations of CO(3-2) in a gas-poor dwarf galaxy, uncovering filamentary structures and their role in fueling star formation.

Findings

Dense molecular clouds are located in extended filaments.

Filaments appear to be infalling, possibly fueling star formation.

CO(3-2) emission is concentrated in the starburst region and correlates with radio emission.

Abstract

We report ALMA observations of $^{12}$CO(3-2) and $^{13}$CO(3-2) in the gas-poor dwarf galaxy NGC 5253. These 0.3"(5.5 pc) resolution images reveal small, dense molecular gas clouds that are located in kinematically distinct, extended filaments. Some of the filaments appear to be falling into the galaxy and may be fueling its current star formation. The most intense CO(3-2) emission comes from the central $\sim$100 pc region centered on the luminous radio-infrared HII region known as the supernebula. The CO(3-2) clumps within the starburst region are anti-correlated with H$\alpha$ on $\sim$5 pc scales, but are well-correlated with radio free-free emission. Cloud D1, which enshrouds the supernebula, has a high $^{12}$CO/$^{13}$CO ratio, as does another cloud within the central 100 pc starburst region, possibly because the clouds are hot. CO(3-2) emission alone does not allow determination of cloud masses as molecular gas temperature and column density are degenerate at the observed brightness, unless combined with other lines such as $^{13}$CO.