湍流磁超临界分子云数值模拟中的核寿命统计
Statistics of Core Lifetimes in Numerical Simulations of Turbulent, Magnetically Supercritical Molecular Clouds
摘要：
我们提出的测量的平均致密的核心寿命的磁超临界，湍流，等温分子云的数值模拟，以比较与观测测定。“星前”寿命（作为核心内的平均密度的函数给出，这反过来又由用于定义它们的密度阈值n_thr确定）与观测报告的值一致，范围从几个到几个自由落体时间。我们还提出了估计的核心在“星前”，“恒星”和“失败”（这些核心重新分散回环境）阶段的分数作为n_thr的函数。由于其分辨率的限制，在模拟中间接测量的数量比。我们的方法包含一个自由参数，一个原恒星对象的寿命t_yso（0类+I类阶段），这是在模拟领域之外。假设t_yso = 0.46 Myr，我们得到的无星核与恒星核的数量比在n_thr = 1.5 x 10^4 cm^-3时为4-5，在n_thr = 1.2 x 10^5 cm^-3时为1，这与观测结果也是一致的。我们还发现，当n_thr = 1.5 x 10^4 cm^-3时，破裂核的质量与恒星核的质量相当，但当n_thr = 1.2 x 10^5 cm^-3时，破裂核的质量可以忽略不计，这与最近的观测结果一致，即在后一种密度下，破裂核的质量一般由引力支配。我们的结论是注意到，核心收缩和崩溃的时间尺度几乎是相同的亚临界，双极扩散介导的恒星形成模型，在湍流超临界云的恒星形成模型，并在前两者之间的模型，目前接受的值的云的磁临界。
英文摘要：
We present measurements of the mean dense core lifetimes in numerical simulations of magnetically supercritical, turbulent, isothermal molecular clouds, in order to compare with observational determinations. "Prestellar" lifetimes (given as a function of the mean density within the cores, which in turn is determined by the density threshold n_thr used to define them) are consistent with observationally reported values, ranging from a few to several free-fall times. We also present estimates of the fraction of cores in the "prestellar", "stellar'', and "failed" (those cores that redisperse back into the environment) stages as a function of n_thr. The number ratios are measured indirectly in the simulations due to their resolution limitations. Our approach contains one free parameter, the lifetime of a protostellar object t_yso (Class 0 + Class I stages), which is outside the realm of the simulations. Assuming a value t_yso = 0.46 Myr, we obtain number ratios of starless to stellar cores ranging from 4-5 at n_thr = 1.5 x 10^4 cm^-3 to 1 at n_thr = 1.2 x 10^5 cm^-3, again in good agreement with observational determinations. We also find that the mass in the failed cores is comparable to that in stellar cores at n_thr = 1.5 x 10^4 cm^-3, but becomes negligible at n_thr = 1.2 x 10^5 cm^-3, in agreement with recent observational suggestions that at the latter densities the cores are in general gravitationally dominated. We conclude by noting that the timescale for core contraction and collapse is virtually the same in the subcritical, ambipolar diffusion-mediated model of star formation, in the model of star formation in turbulent supercritical clouds, and in a model intermediate between the previous two, for currently accepted values of the clouds' magnetic criticality.
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