Large-scale Molecular Gas Distribution in the M17 Cloud Complex: Dense Gas Conditions of Massive Star Formation?
Abstract
The non-uniform distribution of gas and protostars in molecular clouds is caused by combinations of various physical processes that are difficult to separate. We explore this non-uniform distribution in the M17 molecular cloud complex that hosts massive star formation activity using the 12CO (J = 1-0) and 13CO (J = 1-0) emission lines obtained with the Nobeyama 45 m telescope. Differences in clump properties such as mass, size, and gravitational boundedness reflect the different evolutionary stages of the M17-H II and M17-IRDC clouds. Clumps in the M17-H II cloud are denser, more compact, and more gravitationally bound than those in M17-IRDC. While M17-H II hosts a large fraction of very dense gas (27%) that has a column density larger than the threshold of ∼1 g cm-2 theoretically predicted for massive star formation, this very dense gas is deficient in M17-IRDC (0.46%). Our HCO+ (J = 1-0) and HCN (J = 1-0) observations with the Taeduk Radio Astronomy Observatory 14 m telescope trace all gas with a column density higher than 3 × 1022 cm-2, confirming the deficiency of high-density (≳105 cm-3) gas in M17-IRDC. Although M17-IRDC is massive enough to potentially form massive stars, its deficiency of very dense gas and gravitationally bound clumps can explain the current lack of massive star formation.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2020
- DOI:
- 10.3847/1538-4357/ab700a
- arXiv:
- arXiv:2001.09559
- Bibcode:
- 2020ApJ...891...66N
- Keywords:
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- Star formation;
- Giant molecular clouds;
- Diffuse molecular clouds;
- Interstellar medium;
- Protostars;
- 1569;
- 653;
- 381;
- 847;
- 1302;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- We welcome all comments to make the paper better. Please send comments to my email. Thank you