论文标题
在宇宙时间模拟星团：ii。从分子云中逃脱电离光子的分数
Simulating Star Clusters Across Cosmic Time: II. Escape Fraction of Ionizing Photons from Molecular Clouds
论文作者
论文摘要
我们使用一组高分辨率的辐射 - 磁性 - 磁性 - 氢动力学模拟了自我散热，湍流的分子云。在HE，Ricotti和Geen（2019）中提出的这些模拟中，单个大型恒星的形成得到了很好的解决，并且他们在主序列上的UV辐射反馈和寿命是自言自语的。我们发现，从分子云中电离辐射的逃逸分数，$ \ langle f _ {\ rm Esc}^{\ ScriptScriptScriptStystyle \ rm mc} \ rangle $，随着星团的质量的增加而减小，随着星团的质量而降低。在本地宇宙中通常发现的具有密度的分子云具有可忽略的$ \ langle f _ {\ rm Esc}^{\ scriptScriptStryle \ rm mc} \ rangle $，范围在$ 0.5 \％\％$之间，至$ 5 \％$。十次密集的分子云具有$ \ langle f _ {\ rm eSc}^{\ scriptScriptScriptStryle \ rm mc} \ rangle \ rangle \大约10 \％ - 20 \％$，而$ 100 \ times $ $ $ denser $ denser云产生了球形的群集群集，$ \ langle f _ { ESC}^{\ ScriptScriptStyle \ rm mc} \ rangle \左右20 \％-60 \％$。我们发现$ \ langle f _ {\ rm esc}^{\ scriptScriptStystyle \ rm mc} \ rangle $增加随着气体金属性的减少，即使忽略灰尘灭绝，由于更强的辐射反馈。但是，由于恒星形成效率降低，逃逸电离光子的总数随着金属性的降低而减小。我们得出的结论是，$ z> 6 $的电源源必须是在分子云中形成的非常紧凑的恒星簇，比当今的宇宙大约是$ 100 \ tims $浓度，这导致了旧的球形簇祖细胞的大量产生。
We calculate the hydrogen and helium-ionizing radiation escaping star-forming molecular clouds, as a function of the star cluster mass and compactness, using a set of high-resolution radiation-magneto-hydrodynamic simulations of star formation in self-gravitating, turbulent molecular clouds. In these simulations, presented in He, Ricotti and Geen (2019), the formation of individual massive stars are well resolved, and their UV radiation feedback and lifetime on the main sequence are modeled self-consistently. We find that the escape fraction of ionizing radiation from molecular clouds, $\langle f_{\rm esc}^{\scriptscriptstyle \rm MC}\rangle$, decreases with increasing mass of the star cluster and with decreasing compactness. Molecular clouds with densities typically found in the local Universe have negligible $\langle f_{\rm esc}^{\scriptscriptstyle \rm MC}\rangle$, ranging between $0.5\%$ to $5\%$. Ten times denser molecular clouds have $\langle f_{\rm esc}^{\scriptscriptstyle \rm MC}\rangle \approx 10\%-20\%$, while $100\times$ denser clouds, which produce globular cluster progenitors, have $\langle f_{\rm esc}^{\scriptscriptstyle \rm MC}\rangle \approx 20\%-60\%$. We find that $\langle f_{\rm esc}^{\scriptscriptstyle \rm MC}\rangle$ increases with decreasing gas metallicity, even when ignoring dust extinction, due to stronger radiation feedback. However, the total number of escaping ionizing photons decreases with decreasing metallicity because the star formation efficiency is reduced. We conclude that the sources of reionization at $z>6$ must have been very compact star clusters forming in molecular clouds about $100\times$ denser than in today's Universe, which leads to a significant production of old globular clusters progenitors.
