Abstract

We report the first CO detection in Leo T, representing the most extreme observation of carbon monoxide molecules in the lowest stellar mass gas-rich dwarf galaxy (M∗ ∼ 105 M⊙) known to date. We acquired and present new Atacama Compact Array (ACA) 12CO(J = 1-0) data within our CHIMERA Survey project for the central region of Leo T, a metal-poor ([M/H]∼-1.7) dwarf in the Milky Way (MW) outskirts. We identified three compact molecular clouds (< 13 pc) with estimated upper limit virial masses of Mmol ∼- 103 M⊙ each and a total of 1.4 ± 0.4 × 104 M⊙, corresponding to ∼3% of the total gas mass. We obtained CO-to-H2 conversion factors (αCO) as high as ∼ 155 M⊙(K km s-1 pc2)-1 and mean molecular gas surface densities of Σmol ∼ 9 M⊙ pc-2 that are consistent with values found in dwarf galaxies with extremely low metal content. All CO clouds are shifted (∼60 pc) from the stellar population centers, and only one cloud appears within the densest HI region. Two clouds have velocity offsets with the HI of Δvlos ∼ + 13 km s-1 being within twice the velocity dispersion (Δvlos/σHI, los ∼ 2) and probably bound. However, the northern cloud is faster (Δvlos ∼ + 57 km s-1); our models with low halo masses (Mh ≲ 109 M⊙) result in unbound orbits, suggesting that this material is likely being expelled from the dwarf, providing evidence for molecular gas depletion. These properties reveal a perturbed dynamics intertwined with star formation processes in low-mass dwarf galaxies, supporting a scenario of episodic bursts until they are fully quenched by the MW environment. © The Authors 2025.