ULTRAVIOLET ESCAPE FRACTIONS FROM GIANT MOLECULAR CLOUDS DURING EARLY CLUSTER FORMATION
ULTRAVIOLET ESCAPE FRACTIONS FROM GIANT MOLECULAR CLOUDS DURING EARLY CLUSTER FORMATION
复制标题
早期团簇形成过程中从巨型分子云中逸出的紫外线分数
DOI：
10.3847/1538-4357/834/1/40
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
R. Klessen
中科院分区：
文献类型：
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作者：
Corey S. Howard;R. Pudritz;R. Klessen
分子云的紫外光子逃逸率是理解星际介质电离和河外过程（如宇宙再电离）的关键参数。我们提出的电离光子通量和相应的光子逃逸分数（fesc）所产生的后果，星星集群形成的湍流，106 M的巨分子云，模拟使用代码FLASH。我们利用下沉粒子来代表年轻的恒星形成的集群，再加上辐射传输计划来计算出的紫外线通量。我们发现，电离光子通量跨越云边界是高度可变的时间和空间，由于干预气体的湍流性质。逃逸光子的比例在前2.5百万年保持在1.5%，随后在3.25和3.8百万年出现两个明显的峰值，最大fesc分别为30%和37%。这些峰值是由于形成了大的H ii区域，这些区域扩展到较低密度的区域，其中一些到达云表面。然而，这些阶段是短暂的，和fesc急剧下降的H II区域淬火通过高密度的材料，由于云的湍流性质的中心集群。我们发现一个平均fesc的15%的因素，两个变化超过1万年的时间尺度。我们的研究结果表明，假设一个单一的fesc值从分子云一般是一个穷人的近似，系统的动态演化导致大的时间变化。
The UV photon escape fraction from molecular clouds is a key parameter for understanding the ionization of the interstellar medium and extragalactic processes such as cosmic reionization. We present the ionizing photon flux and the corresponding photon escape fraction (fesc) arising as a consequence of star cluster formation in a turbulent, 106 M⊙ giant molecular cloud, simulated using the code FLASH. We make use of sink particles to represent young, star-forming clusters coupled with a radiative transfer scheme to calculate the emergent UV flux. We find that the ionizing photon flux across the cloud boundary is highly variable in time and space due to the turbulent nature of the intervening gas. The escaping photon fraction remains at ∼5% for the first 2.5 Myr, followed by two pronounced peaks at 3.25 and 3.8 Myr with a maximum fesc of 30% and 37%, respectively. These peaks are due to the formation of large H ii regions that expand into regions of lower density, some of which reaching the cloud surface. However, these phases are short-lived, and fesc drops sharply as the H ii regions are quenched by the central cluster passing through high-density material due to the turbulent nature of the cloud. We find an average fesc of 15% with factor of two variations over 1 Myr timescales. Our results suggest that assuming a single value for fesc from a molecular cloud is in general a poor approximation, and that the dynamical evolution of the system leads to large temporal variation.