The Dense-gas Mass versus Star Formation Rate Relation: A Misleading Linearity?
The Dense-gas Mass versus Star Formation Rate Relation: A Misleading Linearity?
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致密气体质量与恒星形成率的关系：误导性的线性？
DOI：
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发表时间：
2017
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影响因子：
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通讯作者：
G. Parmentier
中科院分区：
文献类型：
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作者：
G. Parmentier
当分子团块的体积密度分布为等温球（即）时，我们建立了分子团块的恒星形成关系，该关系依赖于它们的致密气体质量。致密气体定义为体积密度高于某一阈值的气体（即HCN（1-0）映射气体）。我们将集群划分为两个区域：密集的内部区域（在哪里）和低密度的外围区域（在哪里）。我们发现，即使超过一半的星团恒星形成活动发生在低密度的外围，星团的总恒星形成率也与它们密集的内部区域的质量成线性关系。因此，我们强调，线性恒星形成关系并不一定意味着恒星形成只发生在由恒星形成关系给出质量的气体中。当我们考虑到在低密度外围形成恒星的密集碎片（例如，核心，纤维）的质量时，恒星形成关系的线性得到了加强，而我们采用的团块密度曲线并不能解决这些问题。我们还发现，当考虑致密气体时，恒星形成关系比考虑所有团块气体时要紧密得多，就像在银河面分子云中观察到的那样。当团块没有低密度的外围（即它们只由致密气体组成）时，恒星形成关系变得超线性并逐渐变宽。
We model the star formation relation of molecular clumps in dependence of their dense-gas mass when their volume density profile is that of an isothermal sphere (i.e., ). Dense gas is defined as gas whose volume density is higher than a threshold (i.e., HCN(1-0)-mapped gas). We divide the clump into two regions: a dense inner region (where ), and low-density outskirts (where ). We find that the total star formation rate of clumps scales linearly with the mass of their dense inner region, even when more than half of the clump star formation activity takes place in the low-density outskirts. We therefore emphasize that a linear star formation relation does not necessarily imply that star formation takes place exclusively in the gas whose mass is given by the star formation relation. The linearity of the star formation relation is strengthened when we account for the mass of dense fragments (e.g., cores, fibers) seeding star formation in the low-density outskirts, and which our adopted clump density profile does not resolve. We also find that the star formation relation is significantly tighter when considering the dense gas than when considering all the clump gas, as observed for molecular clouds of the Galactic plane. When the clumps have no low-density outskirts (i.e., they consist of dense gas only), the star formation relation becomes superlinear and progressively wider.