How Galactic Environment Affects the Dynamical State of Molecular Clouds and Their Star Formation Efficiency
How Galactic Environment Affects the Dynamical State of Molecular Clouds and Their Star Formation Efficiency
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DOI：
10.3847/1538-4357/ab3a43
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发表时间：
2019-08
期刊：
影响因子：
--
通讯作者：
A. Schruba;J. Kruijssen;A. Leroy
中科院分区：
文献类型：
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作者：
A. Schruba;J. Kruijssen;A. Leroy
我们研究了分子云的动力学状态与宿主星系环境的关系，以及这对银河系和七个邻近星系的星星形成效率（SFE）的影响。我们编译测量分子云和宿主星系的属性，并确定整个星系和不同的子区域内的质量加权平均云属性。我们发现分子云处于环境压力平衡的维里平衡，其中气体丰富，分子为主，高压区域的云接近自我维里化，而气体贫乏，原子为主，低压环境中的云实现内部动力学压力和外部压力之间的平衡。分子云的单位自由落体时间的超临界流体能量很低，约为0.1%-1%，并表现出2 dex的系统变化，作为维里参数和宿主星系环境的函数。在低气压环境中观察到的云的趋势--就像太阳附近--与最先进的星星形成的双折射调节模型很好地匹配。然而，这些模型大大高估了低观测到的SFE云在高压环境中，这表明这些模型尚未考虑的其他物理参数的重要性。
We investigate how the dynamical state of molecular clouds relates to host galaxy environment and how this impacts the star formation efficiency (SFE) in the Milky Way and seven nearby galaxies. We compile measurements of molecular cloud and host galaxy properties, and determine mass-weighted mean cloud properties for entire galaxies and distinct subregions within. We find molecular clouds to be in ambient pressure-balanced virial equilibrium, where clouds in gas-rich, molecular-dominated, high-pressure regions are close to self-virialization, whereas clouds in gas-poor, atomic-dominated, low-pressure environments achieve a balance between their internal kinetic pressure and external pressure from the ambient medium. The SFE per free-fall time of molecular clouds is low, ∼0.1%–1%, and shows systematic variations of 2 dex as a function of the virial parameter and host galactic environment. The trend observed for clouds in low-pressure environments—as the solar neighborhood—is well matched by state-of-the-art turbulence-regulated models of star formation. However, these models substantially overpredict the low observed SFEs of clouds in high-pressure environments, which suggest the importance of additional physical parameters not yet considered by these models.