On the Spatial Distribution of <sup>13</sup>CO Structures within <sup>12</sup>CO Molecular Clouds

Yuan, Lixia; Yang, Ji; Du, Fujun; Liu, Xunchuan; Su, Yang; Yan, Qing-Zeng; Chen, Xuepeng; Sun, Yueqiang; Zhang, S. B.; Zhou, Xin; Ma, Yuehui

doi:10.3847/1538-4357/acac26

“…The reason we utilize 13 CO data for cloud identification is that 13 CO is usually optically thin (Figure 5(b); see also Wang et al 2023a). In addition, statistics of large MC samples show that 13 CO can trace the main structures of MCs (Su et al 2020;Wang et al 2023a;Yuan et al 2023). Moreover, the 13 CO spectral line profile is velocity separated compared to the 12 CO spectral line profile for MCs with multivelocity components.…”

Section: Cloud Identificationmentioning

confidence: 98%

Distribution and Properties of Molecular Gas toward the Monoceros OB1 Region

Zhuang,

Su,

Zhang

et al. 2024

ApJ

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We perform a comprehensive CO study toward the Monoceros OB1 (Mon OB1) region based on the Milky Way Imaging Scroll Painting survey at an angular resolution of about 50″. The high-sensitivity data, together with the high dynamic range, show that molecular gas in the 8° × 4° region displays complicated hierarchical structures and various morphology (e.g., filamentary, cavity-like, shell-like, and other irregular structures). Based on Gaussian decomposition and clustering for 13CO data, a total of 263 13CO structures are identified in the whole region, and 88% of raw data flux is recovered. The dense gas with relatively high column density from the integrated CO emission is mainly concentrated in the region where multiple 13CO structures are overlapped. Combining the results of 32 large 13CO structures with distances from Gaia DR3, we estimate an average distance of 729 − 45 + 45 pc for the giant molecular cloud (GMC) complex. The total mass of the GMC complex traced by 12CO, 13CO, and C18O is 1.1 × 105 M ⊙, 4.3 × 104 M ⊙, and 8.4 × 103 M ⊙, respectively. The dense gas fraction shows a clear difference between Mon OB1 GMC East (12.4%) and Mon OB1 GMC West (3.3%). Our results show that the dense gas environment is closely linked to the nearby star-forming regions. On the other hand, star-forming activities have a great influence on the physical properties of the surrounding molecular gas (larger velocity dispersion, higher temperatures, more complex velocity structures, etc.). We also discuss the distribution/kinematics of molecular gas associated with nearby star-forming activities.

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“…25, and the line-of-sight velocity of −95 km s −1 < V LSR < 25 km s −1 . These 12 CO and 13 CO lines emission data also have been analyzed in our previous series of works in Yuan et al (2021Yuan et al ( , 2022Yuan et al ( , 2023aYuan et al ( , 2023b.…”

Section: Datamentioning

confidence: 99%

Relative Velocities between ¹³CO Structures within ¹²CO Molecular Clouds

Yuan,

Yang,

Chen

et al. 2024

AJ

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Velocity fields of molecular clouds (MCs) can provide crucial information on the merger and split between clouds, as well as their internal kinematics and maintenance, energy injection and redistribution, and even star formation within clouds. Using the CO spectral lines data from the Milky Way Imaging Scroll Painting survey, we measure the relative velocities along the line of sight (ΔV LOS) between 13CO structures within 12CO MCs. Emphasizing MCs with double and triple 13CO structures, we find that approximately 70% of ΔV LOS values are less than ∼1 km s−1, and roughly 10% of values exceed 2 km s−1, with a maximum of ∼5 km s−1. Additionally, we compare ΔV LOS with the internal velocity dispersion of 13CO structures ( σ 13 CO , in ) and find that about 40% of samples in either double or triple regime display distinct velocity discontinuities, i.e., the relative velocities between 13CO structures are larger than the internal line widths of 13CO structures. Among these 40% samples in the triple regime, 33% exhibit signatures of combinations through the two-body motion, whereas the remaining 7% show features of configurations through the multiple-body motion. The ΔV LOS distributions for MCs with double and triple 13CO structures are similar, as well as their ΔV LOS/ σ 13 CO , in distributions. This suggests that relative motions of 13CO structures within MCs are random and independent of cloud complexities and scales.

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“…The universality of the exponential shape of flux-intensity relations may be traced back to the formation process of molecular clouds. For instance, Yuan et al (2023aYuan et al ( , 2023b proposed a picture that large-scale molecular clouds are formed by merging (coagulation). In this scenario, the flux-intensity relation constructed from a collection of individual clouds is also likely to show an exponential shape.…”

Section: Implications Of Flux-intensity Relationsmentioning

confidence: 99%

On the Flux–Intensity Relation of Molecular Clouds

Yan,

Yang,

Su

et al. 2024

ApJL

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In this work, we report a study on the relationship between flux and intensity for molecular clouds. Our analysis is established on high-quality CO images from the Milky Way Imaging Scroll Painting project. The new flux–intensity relation characterizes the flux variation of molecular clouds above specific intensity levels. We found that the flux–intensity relation exhibits two prominent features. First, the flux–intensity relation generally follows exponential shapes; second, hierarchical structures of molecular clouds are imprinted on flux–intensity relations. Specifically, 12CO flux–intensity relations are composed of one or more exponential segments, and for molecular clouds with segmented flux–intensity relations, the edge and the flux of the high-temperature component are strikingly consistent with 13CO emission. Further analysis shows that a similar relationship also exists between 13CO flux–intensity relations and C18O emission. The mean brightness temperature of molecular clouds is tightly associated with the decay rate of flux, the break temperature of exponential segments, and, to a certain extent, the flux fraction of the high-temperature component. Broadly, the flux–intensity relation of a molecular tracer, either in optically thick or in optically thin cases, has the capability to outline the silhouette of internal structures of molecular clouds, proving to be a potent tool for probing structures of molecular clouds.

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On the Spatial Distribution of ¹³CO Structures within ¹²CO Molecular Clouds

Cited by 5 publications

References 86 publications

Distribution and Properties of Molecular Gas toward the Monoceros OB1 Region

Distribution and Properties of Molecular Gas toward the Monoceros OB1 Region

Relative Velocities between ¹³CO Structures within ¹²CO Molecular Clouds

On the Flux–Intensity Relation of Molecular Clouds

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On the Spatial Distribution of 13CO Structures within 12CO Molecular Clouds

Cited by 5 publications

References 86 publications

Distribution and Properties of Molecular Gas toward the Monoceros OB1 Region

Distribution and Properties of Molecular Gas toward the Monoceros OB1 Region

Relative Velocities between 13CO Structures within 12CO Molecular Clouds

On the Flux–Intensity Relation of Molecular Clouds

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On the Spatial Distribution of ¹³CO Structures within ¹²CO Molecular Clouds

Relative Velocities between ¹³CO Structures within ¹²CO Molecular Clouds