Conditions for HD Cooling in the First Galaxies Revisited: Interplay between Far-Ultraviolet and Cosmic Ray Feedback in Population III Star Formation
Conditions for HD Cooling in the First Galaxies Revisited: Interplay between Far-Ultraviolet and Cosmic Ray Feedback in Population III Star Formation
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重新审视第一个星系中高清冷却的条件：远紫外线和宇宙射线反馈在族 III 恒星形成中的相互作用
DOI：
10.1093/mnras/stu1042
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发表时间：
2014
影响因子：
4.8
通讯作者：
K. Omukai
中科院分区：
文献类型：
--
作者：
D. Nakauchi;K. Inayoshi;K. Omukai
HD控制着具有增强电离的原始云的冷却，例如结构形成中的冲击加热云或超新星遗迹，Pop III星的遗迹Hiirregions和具有宇宙射线（CR）照射的云。在那里，温度下降到几十K，特征恒星质量下降到100 M <$A，与第一颗由未受干扰的原始云形成的恒星（100 M <$A）形成对比。然而，在没有CR照射的情况下，即使是弱的远紫外（FUV）照射也会抑制HD的形成/冷却。在这里，我们研究条件HD冷却原始云，包括FUV和CR反馈。坍缩初期，激波压缩气体随密度增加而冷却，而遗迹Hiiregion气体密度不变而冷却。此外，冲击往往发生在比Hiiregions更密集的环境中。由于更高的柱密度和更有效的屏蔽，在激波压缩气体中HD冷却的临界FUV强度比在遗迹Hiirregions中的高10倍。因此，在冲击压缩气体中，临界FUV强度超过背景水平的大部分红移，我们认为（6 <$z <$15），而在遗迹HiII区，HD冷却变得有效后，CR强度增加到足够的atz <$10。我们的研究结果表明，质量较小的（100万吨）Pop III星可能比以前认为的更常见，可能是Pop III星的主要群体。
HD dominates the cooing of primordial clouds with enhanced ionization, e.g. shock-heated clouds in structure formation or supernova remnants, relic Hiiregions of Pop III stars and clouds with cosmic ray (CR) irradiation. There, the temperature decreases to several 10 K and the characteristic stellar mass decreases to ∼10 M⊙, in contrast with first stars formed from undisturbed pristine clouds (∼100 M⊙). However, without CR irradiation, even weak far-ultraviolet (FUV) irradiation suppresses HD formation/cooling. Here, we examine conditions for HD cooling in primordial clouds including both FUV and CR feedback. At the beginning of collapse, the shock-compressed gas cools with its density increasing, while the relic Hiiregion gas cools at a constant density. Moreover, shocks tend to occur in denser environments than Hiiregions. Owing to the higher column density and the more effective shielding, the critical FUV intensity for HD cooling in a shock-compressed gas becomes ∼10 times higher than that in relic Hiiregions. Consequently, in the shock-compressed gas, the critical FUV intensity exceeds the background level for most of the redshift we consider (6 ≲z≲ 15), while in relic Hiiregions, HD cooling becomes effective after the CR intensity increases enough atz≲ 10. Our result suggests that less massive (∼10 M⊙) Pop III stars may be more common than previously considered and could be the dominant population of Pop III stars.