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Abstract We report a CO(J= 3−2) detection of 23 molecular clouds in the extended ultraviolet (XUV) disk of the spiral galaxy M83 with the Atacama Large Millimeter/submillimeter Array. The observed 1 kpc2region is at about 1.24 times the optical radius (R25) of the disk, where CO(J= 2–1) was previously not detected. The detection and nondetection, as well as the level of star formation (SF) activity in the region, can be explained consistently if the clouds have the mass distribution common among Galactic clouds, such as Orion A—with star-forming dense clumps embedded in thick layers of bulk molecular gas, but in a low-metallicity regime where their outer layers are CO-deficient and CO-dark. The cloud and clump masses, estimated from CO(3−2), range from 8.2 × 102to 2.3 × 104M⊙and from 2.7 × 102to 7.5 × 103M⊙, respectively. The most massive clouds appear similar to Orion A in star formation activity as well as in mass, as expected if the cloud mass structure is common. The overall low SF activity in the XUV disk could be due to the relative shortage of gas in the molecular phase. The clouds are distributed like chains up to 600 pc (or longer) in length, suggesting that the trigger of cloud formation is on large scales. The common cloud mass structure also justifies the use of high-JCO transitions to trace the total gas mass of clouds, or galaxies, even in the high-zuniverse. This study is the first demonstration that CO(3−2) is an efficient tracer of molecular clouds even in low-metallicity environments.
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This content will become publicly available on June 30, 2026
High-velocity Molecular Clouds in M83
Abstract High-velocity clouds (HVCs), which are gas clouds moving at high velocity relative to the galactic disk, may play a critical role in galaxy evolution, potentially supplying gas to the disk and triggering star formation. In this study, we focus on the nearby face-on barred spiral galaxy M83, where high-spatial-resolution, high-sensitivity CO(1–0) data are available. We identified molecular clouds and searched for clouds with velocities deviating by more than 50 km s−1from the disk velocity field as HVCs. A total of 10 HVCs were detected—9 redshifted and 1 blueshifted—clearly highlighting an asymmetry in their velocity distribution. These HVCs have radii of 30–80 pc, masses on the order of 105M⊙, and velocity dispersions of 3–20 km s−1, displaying a tendency toward higher velocity dispersion compared to disk molecular clouds in M83. Most of the HVCs do not overlap with the candidates of supernova remnants, and the energy needed to drive HVCs at such high velocities exceeds single supernova energy. Together with the asymmetry in their velocity distribution, we thus conclude that most of the HVCs found in this study are inflow from outside the M83’s disk.
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- PAR ID:
- 10649865
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 987
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 69
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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