Evolving molecular cloud structure and the column density probability distribution function
Evolving molecular cloud structure and the column density probability distribution function
复制标题
演化的分子云结构和柱密度概率分布函数
DOI：
--
复制
发表时间：
2014
期刊：
影响因子：
--
通讯作者：
A. Sills
中科院分区：
文献类型：
--
作者：
R. L. Ward;J. Wadsley;A. Sills
分子云的结构可以用质量表面密度的概率分布函数(PDF)来表征。特别是，分布的性质可以揭示分子云中存在的湍流和恒星形成的性质。在这篇文章中，我们探索了这些结构特征是如何随时间演变的，以及它们如何与分子云的合成柱状密度图的样本测量的各种云属性相关。我们发现，随着云的演化，其列密度Pdf的峰值将向低于观测探测阈值的表面密度移动，导致潜在的对数正态分布，而这种分布在后期实际上已经丢失。我们的结果解释了为什么某些活跃的恒星形成、动力学上较老的云，如猎户座分子云，在它们的列密度PDF中似乎没有任何对数正态分布的证据。我们还研究了我们的模拟云样本的幂律尾部的斜率和偏离点的演化，表明这两个性质都趋向于恒定值，从而将分子云的柱密度结构与恒星形成的表面密度阈值联系起来。
The structure of molecular clouds can be characterized with the probability distribution function (PDF) of the mass surface density. In particular, the properties of the distribution can reveal the nature of the turbulence and star formation present inside the molecular cloud. In this paper, we explore how these structural characteristics evolve with time and also how they relate to various cloud properties as measured from a sample of synthetic column density maps of molecular clouds. We find that, as a cloud evolves, the peak of its column density PDF will shift to surface densities below the observational threshold for detection, resulting in an underlying lognormal distribution which has been effectively lost at late times. Our results explain why certain observations of actively star-forming, dynamically older clouds, such as the Orion molecular cloud, do not appear to have any evidence of a lognormal distribution in their column density PDFs. We also study the evolution of the slope and deviation point of the power-law tails for our sample of simulated clouds and show that both properties trend towards constant values, thus linking the column density structure of the molecular cloud to the surface density threshold for star formation.