The CHIMERA Survey: The first CO detection in Leo T, the lowest mass known galaxy still hosting cold molecular gas
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Date
2025
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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 ∼ 5 × 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....
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Galaxies dwarf, Galaxies evolution, Galaxies ISM, Local Group