Cloud Properties and Correlations with Star Formation in Self-consistent Simulations of the Multiphase ISM
Cloud Properties and Correlations with Star Formation in Self-consistent Simulations of the Multiphase ISM
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DOI：
10.3847/1538-4357/ab989c
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发表时间：
2019-11
期刊：
影响因子：
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通讯作者：
S. Mao;E. Ostriker;Chang-Goo Kim
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文献类型：
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作者：
S. Mao;E. Ostriker;Chang-Goo Kim
我们应用重力和密度为基础的方法，以确定云的恒星形成，多相星际介质（ISM）的自洽数值模拟，并比较其性能和全球相关性的星星形成率（SFR）随着时间的推移。基于引力的方法识别出在密度下有质量的束缚物体，维里参数αv <$0.5 -5。对于由密度阈值定义的云，平均维里参数减小，而真正结合的物质的比例增加，随着增加。令人惊讶的是，由密度阈值定义的云即使在αv < 2时也可以是未绑定的，并且大质量云（）通常是未绑定的。这表明传统的αv充其量只是ISM中有界性的近似度量。所有的云都有内部的湍流运动，随着尺寸的增加而增加，类似于观察到的关系。束缚结构只占模拟总质量的一小部分，每自由落体时间的星星形成效率为1.04。对于α_0.03 -0.3，随密度阈值的增大而增大。通过对不同时刻和聚集体质量的时间相关性分析表明，星星形成的时间延迟是有限的.和之间的相关性在更高时系统地收紧。考虑到中等密度的气体，选择高维里参数云提高了与SFR的相关性，与以前的工作一致。由于系统的大幅度变化和固有的随机性，即使在高频段，时间色散也是~ 50%。
We apply gravity- and density-based methods to identify clouds in self-consistent numerical simulations of the star-forming, multiphase interstellar medium (ISM) and compare their properties and global correlation with the star formation rate (SFR) over time. The gravity-based method identifies bound objects, which have masses at densities , and virial parameters αv ∼ 0.5–5. For clouds defined by a density threshold , the average virial parameter decreases, and the fraction of material that is genuinely bound increases, with increasing . Surprisingly, clouds defined by density thresholds can be unbound even when αv < 2, and high-mass clouds ( ) are generally unbound. This suggests that the traditional αv is at best an approximate measure of boundedness in the ISM. All clouds have internal turbulent motions increasing with size as , similar to observed relations. Bound structures comprise a small fraction of the total simulation mass and have a star formation efficiency per freefall time ∼ 0.4. For , ∼ 0.03–0.3, increasing with density threshold. A temporal correlation analysis between and aggregate mass at varying shows that time delays to star formation are . The correlation between and systematically tightens at higher . Considering moderate-density gas, selecting against high virial parameter clouds improves correlation with the SFR, consistent with previous work. Even at high , the temporal dispersion in is ∼50%, due to the large-amplitude variations and inherent stochasticity of the system.