剪切—引力转变决定分子云中陡峭的速度弥散—尺度关系：解析公式与观测的对比
Shear-gravity transition determines the steep velocity dispersion-size relation in molecular clouds: confronting analytical formula with observations
AI总结：
该研究提出结合自引力与银河剪切的双组分模型，解释数秒差距以上分子云中观测到的陡峭速度弥散—尺度关系及其约100 pc转变尺度。
摘要：
速度弥散—尺度关系（$σ_{\rm v}\sim R^β$）是星际气体动力学性质的关键指标，其斜率通常被认为是 $β\sim0.5$。近期观测揭示出斜率 $β>0.6$ 的陡峭速度弥散—尺度关系，这无法由仅包含引力（$β\sim0.5$）或剪切（$β\sim1$）的单一机制解释。我们提出一个双组分模型 $σ_{\rm v_{total}} = λ_1 σ_{\rm v_{g}} + λ_2 σ_{\rm v_{shear}} = A[(GM/R)^{\frac{1}{2}} + f(R/t_{\rm shear})]$，用于解释 Miville-Deschênes 等人（2017）、Zhou 等人（2022）和 Sun 等人（2024）等观测中大于几秒差距尺度分子云的陡峭速度弥散—尺度关系。我们发现，在几秒差距以上，较小云的速度弥散主要由自引力引起，而较大云主要受剪切影响；这两个区间通过一个逐渐转变相连接，转变尺度约为100 pc，即银河分子气体盘的标高。云的速度弥散—尺度关系随银心距的变化，源于云内部密度结构和银河系剪切率两者的共同变化。我们的双组分模型刻画了分子气体动力学如何同时受到内部和外部因素影响，并期望将其应用于具有不同物理条件的星系数据，以揭示相关物理机制。
英文摘要：
The velocity dispersion-size relation ($σ_{\rm v}\sim R^β$) is a crucial indicator of the dynamic properties of interstellar gas, where the slope is considered as $β\sim 0.5$. Recent observations reveal a steep velocity dispersion-size relation with the slope $β> 0.6$, which cannot be explained by a single mechanism with only gravity ($β\sim0.5$) or shear ($β\sim 1$). We present a two-component model $σ_{\rm v_{total}} = λ_1 σ_{\rm v_{g}} + λ_2 σ_{\rm v_{shear}} = A[(GM/R)^{\frac{1}{2}} + f(R/t_{\rm shear})]$ to explain the steep velocity dispersion-size relation for clouds larger than several parsecs in observations from e.g. Miville-Deschênes et al. (2017), Zhou et al. (2022) and Sun et al. (2024). We find that, above several parsecs, the velocity dispersion of small clouds is mainly caused by self-gravity, while large clouds are primarily affected by shear, and these two regimes are linked by a gradual transition with a transition scale $\sim100$ pc -- the scale height of the Galactic molecular gas disk. The variation of cloud velocity dispersion-size relation with the Galactocentric distance results from the variation of both cloud internal density structure and Galactic shear rate. Our two-component model captures how the dynamics of the molecular gas can be affected by both internal and external factors, and we expect it to be applied to data from galaxies with different physical conditions to reveal the physics.
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