Molecular Gas Structures traced by ${}^{13}$CO Emission in the 18,190 ${}^{12}$CO Molecular Clouds from the MWISP Survey

Abstract

After the morphological classification of the 18,190 ${}^{12}$CO molecular clouds, we further investigate the properties of their internal molecular gas structures traced by the ${}^{13}$CO($J=$ 1$-$0) line emissions. Using three different methods to extract the ${}^{13}$CO gas structures within each ${}^{12}$CO cloud, we find that $\sim$ 15$\%$ of ${}^{12}$CO clouds (2851) have ${}^{13}$CO gas structures and these ${}^{12}$CO clouds contribute about 93$\%$ of the total integrated flux of ${}^{12}$CO emission. In each of 2851 ${}^{12}$CO clouds with ${}^{13}$CO gas structures, the ${}^{13}$CO emission area generally does not exceed 70$\%$ of the ${}^{12}$CO emission area, and the ${}^{13}$CO integrated flux does not exceed 20$\%$ of the ${}^{12}$CO integrated flux. We reveal a strong correlation between the velocity-integrated intensities of ${}^{12}$CO lines and those of ${}^{13}$CO lines in both ${}^{12}$CO and ${}^{13}$CO emission regions. This indicates the H${}_2$ column densities of molecular clouds are crucial for the ${}^{13}$CO lines emission. After linking the ${}^{13}$CO structure detection rates of the 18,190 ${}^{12}$CO molecular clouds to their morphologies, i.e. nonfilaments and filaments, we find that the ${}^{13}$CO gas structures are primarily detected in the ${}^{12}$CO clouds with filamentary morphologies. Moreover, these filaments tend to harbor more than one ${}^{13}$CO structure. That demonstrates filaments not only have larger spatial scales, but also have more molecular gas structures traced by ${}^{13}$CO lines, i.e. the local gas density enhancements. Our results favor the turbulent compression scenario for filament formation, in which dynamical compression of turbulent flows induces the local density enhancements. The nonfilaments tend to be in the low-pressure and quiescent turbulent environments of the diffuse interstellar medium.

21 pages, 14 Figures; Appendix (17 pages, 19 Figures); Accepted for publication in the journal ApJS

References in corpus (19)

• Star Formation in Disk Galaxies. I. Formation and Evolution of Giant Molecular Clouds via Gravitational Instability and Cloud Collisions
• Dawes Review 4: Spiral Structures in Disc Galaxies
• The Birth of Molecular Clouds: Formation of Atomic Precursors in Colliding Flows
• The Milky Way Imaging Scroll Painting (MWISP): Project Details and Initial Results from the Galactic Longitude of 25.8deg to 49.7deg
• Full-disc ${}^{13}$CO(1-0) mapping across nearby galaxies of the EMPIRE survey and the CO-to-H${}_2$ conversion factor
• Investigating the structure and fragmentation of a highly filamentary IRDC
• Star formation in turbulent molecular clouds with colliding flow
• Classification of Filament Formation Mechanisms in Magnetized Molecular Clouds
• Distances and statistics of local molecular clouds in the first Galactic quadrant
• Dynamical cloud formation traced by atomic and molecular gas
• A Morphological Classification of 18190 Molecular Clouds Identified in ${}^{12}$CO Data from the MWISP Survey
• Edge collapse and subsequent longitudinal accretion in Filament S242
• Velocity structure of the 50 pc-long NGC 6334 filamentary cloud: Hints of multiple compressions and their impact on the cloud properties?
• Distances to molecular clouds in the second Galactic quadrant
• Physical and chemical structure of the Serpens filament -- fast formation and gravity-driven accretion
• The SEDIGISM survey: Molecular cloud morphology. I. Classification and star formation
• VALES VI: ISM enrichment in star-forming galaxies up to z$\sim$0.2 using ${}^{12}$CO(1-0), ${}^{13}$CO(1-0) and C${}^{18}$O(1-0) line luminosity ratios
• Galactic star formation with NIKA2 (GASTON): Filament convergence and its link to star formation
• Sequential Star Formation in the filamentary structures of Planck Galactic cold clump G181.84+0.31

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• 12CO (3-2) High-Resolution Survey (COHRS) of the Galactic Plane: Complete Data Release
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• On the Spatial Distribution of ${}^{13}$CO Structures within ${}^{12}$CO Molecular Clouds
• A three-dimensional reconstruction of the interstellar magnetic field toward a star-forming region