arXiv subjects

Suziye He

Publications and source records attributed to Suziye He.

5 recordsLinked to original sources

arXiv2026

Hierarchical Dynamics within Molecular Clouds: Type 4 Scaling Relations of Molecular Clouds in the Second Galactic Quadrant

We present a statistical study of the hierarchical structure of molecular clouds in the second quadrant of the Galactic midplane (139.75 deg <= l <= 159.75 deg, -5.25 deg <= b <= 8.25 deg), based on high-sensitivity 12CO and 13CO J = 1-0 data from the Milky Way Imaging Scroll Painting survey. Using DBSCAN and a non-binary Dendrogram algorithm, we identify 2,912 13CO clouds. Type 2 (multicloud, single-tracer) scaling relations show arm-dependent trends: the power-law index of the linewidth-size relation is about 0.32 in the Local Arm and about 0.42 in the Perseus and Outer Arms. The classical Keto-Heyer relation is weak in the Local Arm but present in the Perseus and Outer Arms, with a slope of about 0.3. The virial parameter is anti-correlated with cloud size, mass, and surface density, consistent with previous surveys. Type 4 (single-cloud, single-tracer) scaling relations exhibit stronger internal correlations. The linewidth-size index spans about 0.3-0.8 and correlates positively with sonic Mach number, indicating that the relation is not universal but depends on cloud compressibility. While substructures do not follow the conventional surface-density-based Keto-Heyer relation, a volume-density formulation restores a clear virial scaling, with evolutionary tracks aligning along lines of constant virial parameter. Moreover, the structural complexity of molecular clouds, characterized by the relationship between the number of substructures and the min_delta parameter, correlates with surface density rather than sonic Mach number, contrary to results from turbulence-only magnetohydrodynamic simulations. Together, these results are more consistent with a gravity-regulated hierarchical dynamical picture than with a purely turbulence-supported scenario.

astro-ph.GA↗

arXiv2026

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↗

arXiv2025

Examining Turbulence in Galactic Molecular Clouds -- I: A Statistical Analysis of Velocity Structures

We present a systematic analysis of the velocity structure functions (VSFs) of 167 molecular clouds with angular sizes greater than $\sim$176 arcmin$^2$ in three sectors of the Galactic mid-plane. We calculated the 1st- to 3rd-order VSFs and found that 60\% of the VSFs exhibit power-law distributions. The relative power-law exponents are consistent with predictions from intermittent turbulence models. Column density weighting reduces the proportion of power-law VSFs and steepens the VSF slopes, implying a reduction of turbulent energy in high-density regions. All clouds show small-scale intermittency, with slightly stronger intermittency in those molecular clouds showing none power-law VSFs. Negative VSF exponents that may indicate gravitational collapse are not observed in our sample. The scaling exponents of the observed VSFs do not correlate with the virial parameters of the molecular clouds. These two observations suggest that gravity-dominated scales in molecular clouds still need further investigation. Consistent VSF scaling exponents for the molecular clouds with significant power-law VSFs suggest large-scale external driving of turbulence in these molecular clouds. However, the driving mechanisms are likely not universal, as the power-law scaling coefficients in our results show relatively large scatter. The fact that nearly 40\% of the VSFs deviate to some extent from power-law distributions suggests that the influence of local environments on the internal turbulence of molecular clouds may not be negligible.

astro-ph.GA↗

arXiv2024

Hierarchical Structure and Self-gravity in the Maddalena Giant Molecular Cloud

In this work, we present the data from the Milky Way Imaging Scroll Painting (MWISP) project for the Maddalena giant molecular cloud (GMC). We decompose the 13CO emission datacube of the observed region into hierarchical substructures using a modified Dendrogram algorithm. We investigate the statistical properties of these substructures and examine the role that self-gravity plays on various spatial scales. The statistics of the mass (M), radius (R), velocity dispersion (σv), virial parameter (αvir), and sonic Mach number of the substructures are presented. The radius and mass distributions and the σv-R scaling relationship of the substructures resemble those reported in previous studies that use non-hierarchical algorithms to identify the entities. We find that for the hierarchical substructures αvir decreases as the radius or mass of the substructures increases. The majority of the substructures in the quiescent region of Maddalena GMC are not gravitationally bound (αvir > 2), while most of the substructures in the star-forming regions are gravitationally bound (αvir < 2). Furthermore, we find that self-gravity plays an important role on scales of 0.8-4 pc in the IRAS 06453 star-forming region, while it is not an important factor on scales below 5 pc in the non-star-forming region.

astro-ph.GA↗