Modelling population III stars for seminumerical simulations
Modelling population III stars for seminumerical simulations
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DOI：
10.1093/mnras/stab072
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发表时间：
2020-11
影响因子：
4.8
通讯作者：
Toshiyuki Tanaka;K. Hasegawa
中科院分区：
文献类型：
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作者：
Toshiyuki Tanaka;K. Hasegawa
对Pop III恒星(Pop III恒星)产生的21厘米信号进行理论建模是从当前和即将进行的21厘米观测中提取关于Pop III恒星的丰富信息的关键。在这项工作中，我们开发了一个新的Pop III恒星模块，其中一致地结合了电离光子和Lyman-Werner(LW)光子的逃逸部分、UV辐射的光加热和LW反馈。通过将该模块实现到一个公共的21厘米半数值模拟程序21CMFAST中，我们演示了21厘米信号的计算，并研究了POP III恒星模拟的重要性。我们发现，Pop III恒星对宇宙电离的贡献很大程度上取决于逃逸分数的处理。在我们的逃逸分数模型中，POP III恒星几乎没有对再电离做出贡献，因为由于LW反馈，质量较小的光晕不能容纳POP III恒星，因为它们的逃逸分数很高。另一方面，Pop III恒星通过常规的恒定逃逸分数很好地促进了再电离。我们还发现，如果宇宙的电离分数高于约1%，紫外光加热对21厘米的全球信号和21厘米的功率谱有不可忽略的影响。在这种情况下，21厘米全球信号的强度取决于光热效率，因此也取决于Pop III恒星质量。我们的结论是，为了准确地预测未来观测的21厘米可观测值，对POP III恒星进行详细的建模是必不可少的。
Theoretically modelling the 21-cm signals caused by Population III stars (Pop III stars) is the key to extracting fruitful information on Pop III stars from current and forthcoming 21-cm observations. In this work we develop a new module of Pop III stars in which the escape fractions of ionizing photons and Lyman-Werner (LW) photons, photo-heating by UV radiation, and LW feedback are consistently incorporated. By implementing the module into a public 21-cm semi-numerical simulation code, 21CMFAST, we demonstrate 21-cm signal calculations and investigate the importance of Pop III star modelling. What we find is that the contribution from Pop III stars to cosmic reionization significantly depends on the treatment of the escape fraction. With our escape fraction model, Pop III stars hardly contribute to reionization because less massive halos, whose escape fraction are high, cannot host Pop III stars due to LW feedback. On the other hand, Pop III stars well contribute to reionization with the conventional constant escape fraction. We also find that UV photo-heating has non-negligible impact on the 21-cm global signal and the 21-cm power spectrum if the ionization fraction of the Universe is higher than roughly 1 percent. In this case, the strength of the 21-cm global signal depends on the photo-heating efficiency and thus on the Pop III star mass. We conclude that detailed modelling of Pop III stars is imperative to predict 21-cm observables accurately for future observations.