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

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 ∼100 pc region centered on the luminous radio-infrared H ii region known as the supernebula. The CO(3–2) clumps within the starburst region are anti-correlated with H α on ∼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.