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| Autores principales: | , |
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| Formato: | Preprint |
| Publicado: |
2024
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| Acceso en línea: | https://arxiv.org/abs/2406.01542 |
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| _version_ | 1866929371295514624 |
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| author | Bieging, John H. Kong, Shuo |
| author_facet | Bieging, John H. Kong, Shuo |
| contents | This paper presents maps of the J=2-1 transition of CO toward the Draco Nebula Intermediate Velocity Cloud (IVC). The maps cover 8500 square arcmin with a velocity resolution of 0.33 km~s$^{-1}$ and angular resolution of 38", or 0.11 pc at the cloud distance of 600 pc. The mapped area includes all the emission detected by the {\it Herschel} satellite with 250 $μ$m intensity >5 MJy/sr. Previously published observations of the far-IR emission and the 21 cm line of HI are used to derive the column density distribution of H$_2$ and the abundance ratio CO/H$_2$, as well as the distribution of the molecular fraction of hydrogen, which approaches 90\% over much of the brighter parts of the nebula. The CO emission is highly clumpy and closely resembles the structures seen in far-IR images. The kinematics of the CO show supersonic motions between clumps but near-thermal to trans-sonic motions within clumps, consistent with model predictions that the scale length for dissipation of supersonic turbulence should be $\sim0.1$ pc, mediated by kinematic viscosity and/or ambipolar diffusion. Different parts of the nebula show evidence for a spread of molecular formation timescales of a few 10$^5$ years, comparable to the dynamical timescale of the infalling gas. The IVC will likely merge with the Galactic interstellar medium in $\sim 10^7$ years, and the densest clumps may form an unbound cluster of low-mass stars. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2406_01542 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | CO in the Draco Nebula: The Atomic-Molecular Transition Bieging, John H. Kong, Shuo Astrophysics of Galaxies This paper presents maps of the J=2-1 transition of CO toward the Draco Nebula Intermediate Velocity Cloud (IVC). The maps cover 8500 square arcmin with a velocity resolution of 0.33 km~s$^{-1}$ and angular resolution of 38", or 0.11 pc at the cloud distance of 600 pc. The mapped area includes all the emission detected by the {\it Herschel} satellite with 250 $μ$m intensity >5 MJy/sr. Previously published observations of the far-IR emission and the 21 cm line of HI are used to derive the column density distribution of H$_2$ and the abundance ratio CO/H$_2$, as well as the distribution of the molecular fraction of hydrogen, which approaches 90\% over much of the brighter parts of the nebula. The CO emission is highly clumpy and closely resembles the structures seen in far-IR images. The kinematics of the CO show supersonic motions between clumps but near-thermal to trans-sonic motions within clumps, consistent with model predictions that the scale length for dissipation of supersonic turbulence should be $\sim0.1$ pc, mediated by kinematic viscosity and/or ambipolar diffusion. Different parts of the nebula show evidence for a spread of molecular formation timescales of a few 10$^5$ years, comparable to the dynamical timescale of the infalling gas. The IVC will likely merge with the Galactic interstellar medium in $\sim 10^7$ years, and the densest clumps may form an unbound cluster of low-mass stars. |
| title | CO in the Draco Nebula: The Atomic-Molecular Transition |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2406.01542 |