Xiangyu Ou | Searcharxiv

arXiv2025

Examining Turbulence in Galactic Molecular Clouds. II. Turbulence Cascade Beyond the Scale of Giant Molecular Clouds

We use $^{12}$CO (J=1--0) data from the MWISP survey to investigate turbulence in a $\sim$kpc-scale segment of the Local Arm. By slicing the position-position-velocity cube into narrow layers that follow the Galactic-rotation trend in the $L$-$V$ diagram, we find that the structure functions (SFs) and spatial power spectra (SPS) of the $^{12}$CO (J=1--0) line velocity and intensity exhibit consistent scaling behaviors across all layers, demonstrating that the molecular gas forms a single, coherent turbulent field with energy cascading from $\sim 200$~pc down to parsec scales. The SPS power-law slopes of both the intensity and velocity fields approach the values expected from turbulence models. Cloud-to-cloud velocity SFs based on the molecular clouds located in the region follow the same extended self-similarity scaling (ESS) as the pixel-based statistics, indicating that inter-cloud motions are part of the same large-scale turbulent cascade. Together, these results provide direct observational evidence that molecular clouds are not dynamically isolated entities but are embedded within a larger-scale turbulent flow that links galactic dynamics to star formation on cloud scales.

astro-ph.GA↗

arXiv2025

Hierarchical Structure and Self-gravity in the Rosette Molecular Cloud

We analyze the hierarchical structure in the Rosette Molecular Cloud (RMC) using $^{13}$CO J=1-0 data from the Milky Way Imaging Scroll Painting (MWISP) survey with a non-binary Dendrogram algorithm that allows multiple branches to emerge from parent structures. A total of 588 substructures are identified, including 458 leaves and 130 branches. The physical parameters of the substructures, including peak brightness temperature ($T_{\rm peak}$), brightness temperature difference ($T_{\rm diff}$), radius ($R$), mass ($M$), velocity dispersion ($σ_v$), and surface density ($Σ$), are characterized. The $T_{\rm peak}$ and $T_{\rm diff}$ distributions follow exponential functions with characteristic values above $5σ_{\rm RMS}$. The statistical properties and scaling relations, i.e., $σ_v$-$R$, $M$-$R$, and $σ_v$-$RΣ$ relations are in general consistent with those from traditional segmentation methods. The mass and radius follow power-law distributions with exponents of 2.2-2.5, with slightly flatter slopes for substructures inside the HII region. The velocity dispersion scales weakly with radius ($σ_v \propto R^{0.45\pm 0.03}$, $r = 0.58$), but shows a tighter correlation with the product of surface density and size ($σ_v \propto (ΣR)^{0.29\pm 0.01}$, $r = 0.73$). Self-gravitating substructures are found across scales from $\sim$0.2 to 10 pc, and nearly all structures with peak brightness above 4 K are gravitationally bound ($α_{\rm vir} < 2$). The fraction of bound structures increases with mass, size, and surface density, supporting the scenario of global hierarchical collapse (GHC) for the evolution of molecular clouds, in which molecular clouds and their substructures are undergoing multiscale collapse.

astro-ph.GA↗