ALMA Detects CO(3–2) within a Super Star Cluster in NGC 5253

We present observations of CO(3–2) and ¹³CO(3–2) emission near the supernebula in the dwarf galaxy NGC 5253, which contains one of the best examples of a potential globular cluster in formation. The 0.″3 resolution images reveal an unusual molecular cloud, "Cloud D1," that is coincident with the radio-infrared supernebula. The ∼6 pc diameter cloud has a linewidth, Δ v = 21.7 $km{s}^{-1}$, that reflects only the gravitational potential of the star cluster residing within it. The corresponding virial mass is 2.5 × 10⁵ $M_{\odot }$. The cluster appears to have a top-heavy initial mass function, with M _* ≳ 1–2 $M_{\odot }$. Cloud D1 is optically thin in CO(3–2), probably because the gas is hot. Molecular gas mass is very uncertain but constitutes <35% of the dynamical mass within the cloud boundaries. In spite of the presence of an estimated ∼1500–2000 O stars within the small cloud, the CO appears relatively undisturbed. We propose that Cloud D1 consists of molecular clumps or cores, possibly star-forming, orbiting with more evolved stars in the core of the giant cluster.