DISTRIBUTION AND MASS OF DIFFUSE AND DENSE CO GAS IN THE MILKY WAY
Open accessAbstract
Emission from carbon monoxide (CO) is ubiquitously used as a tracer of dense star-forming molecular clouds. There is, however, growing evidence that a significant fraction of CO emission originates from diffuse molecular gas. Quantifying the contribution of diffuse CO-emitting gas is vital for understanding the relation between molecular gas and star formation. We examine the Galactic distribution of two CO-emitting gas components, a high column density component detected in 13 CO and 12 CO, and a low column density component detected in 12 CO, but not in 13 CO. The “diffuse” and “dense” components are identified using a combination of smoothing, masking, and erosion/dilation procedures, making use of three large-scale 12 CO and 13 CO surveys of the inner and outer Milky Way. The diffuse component, which globally represents 25% (1.5 × 10 8 M ⊙) of the total molecular gas mass (6.5 M ⊙), is more extended perpendicular to the Galactic plane. The fraction of diffuse gas increases from ∼10%–20% at a galactocentric radius of 3–4 kpc to 50% at 15 kpc, and increases with decreasing surface density. In the inner Galaxy, a yet denser component traced by CS emission represents 14% of the total molecular gas mass traced by 12 CO emission. Only 14% of the molecular gas mass traced by 12 CO emission is identified as part of molecular clouds in 13 CO surveys by cloud identification algorithms. This study indicates that CO emission not only traces star-forming clouds, but also a significant diffuse molecular ISM component.
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- Authors
- Roman-Duval, J., Heyer, M., Brunt, C. M., Clark, P., Klessen, R., & Shetty, R.
- Affiliations
- Space Telescope Science Institute (US)
- University of Massachusetts Amherst (US)
- University of Exeter (GB)
- Cardiff University (GB)
- Heidelberg University (DE)
- Venue
- The Astrophysical Journal
- Publisher
- American Astronomical Society
- Published
- 2016-02-17
- Volume
- 818
- Issue
- 2
- Pages
- 144
- ISSN
- 0004-637X (ISSN-L)
- 1538-4357
- OpenAlex
- W2230493961
- Cited by
- 92
- References
- 59
- Citations by year
- 2026: 6 · 2025: 9 · 2024: 2 · 2023: 8 · 2022: 8 · 2021: 10 · 2020: 18 · 2019: 11 · 2018: 7 · 2017: 9 · 2016: 4
- FWCI
- 4.94
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Licence
- Locations
- The Astrophysical Journal (publishedVersion)
- ORCA Online Research @Cardiff (Cardiff University) (acceptedVersion)
- arXiv (Cornell University) (submittedVersion)
- Figshare (submittedVersion)
- Open Research Exeter (University of Exeter) (submittedVersion)
- arXiv (Cornell University)
- Topics
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astrophysics and Star Formation Studies
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Galaxies: Formation, Evolution, Phenomena
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Stellar, planetary, and galactic studies
- Keywords
- diffuse molecular gas, dense gas, molecular clouds, carbon monoxide emissions, 13CO, 12CO, molecular gas mass, Milky Way, interstellar medium, star formation, column density, cloud detection, CS emission
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