arXiv 2006.152602020-06astro-ph.GAastro-ph.CO

III星群的恒星形成何时结束？

When did Population III star formation end?

Boyuan Liu, Volker Bromm

备注：: 16+2 pages, 1 table, 15 figures, accepted for publication in MNRAS
DOI：: 10.1093/mnras/staa2143

摘要：

通过将宇宙学模拟数据与半解析模型相结合，构建了一个研究后再电离时期（$z\lesssim 6$）第三星族（PopIII）恒星形成的理论框架.我们发现，由于辐射反馈（即莱曼-沃纳和电离辐射）大规模的晕（$M_{\rm halo}\gtrsim 10^{9}\ \rm M_{\odot}$）是主要的（$\gtrsim 90$ %）主机潜在的Pop III星形成在$z\lesssim 6$，在那里密集的口袋金属贫气体可能生存下来，形成Pop III星，在超新星释放的金属的低效率混合。金属混合不仅是决定Pop III恒星形成何时结束的关键过程，也是决定每个主晕中\textit{active} Pop III恒星的总质量$M_{\rm PopIII}$的关键过程，这是直接探测和识别Pop III主晕的关键参数。这两个方面仍然是不确定的，由于我们有限的知识，金属混合在结构形成。目前的预测范围从早期终止在年底的再电离（$z\sim 5$），以连续的Pop III恒星形成扩展到$z=0$在一个不可忽略的速度$\sim 10^{-7}\ \rm M_{\odot}\ yr^{-1}\ Mpc^{-3}$，与$M_{\rm PopIII}\sim 10^{3}-10^{6}\ \rm M_{\odot}$。这导致了目前和未来的空间望远镜（如HST、WFIRST和JWST）直接探测Pop III宿主$z_{\rm PopIII}\sim 0.5-12.5$的红移极限范围很广，探测率为$\lesssim 0.1-20\ \rm arcmin^{-2}$。我们的模型还预测，宇宙体积的大部分（$\gtrsim 90$ %）被无金属气体占据。测量这种无金属相的体积填充分数可以限制金属混合参数和Pop III星的形成。

英文摘要：

We construct a theoretical framework to study Population III (Pop III) star formation in the post-reionization epoch ($z\lesssim 6$) by combining cosmological simulation data with semi-analytical models. We find that due to radiative feedback (i.e. Lyman-Werner and ionizing radiation) massive haloes ($M_{\rm halo}\gtrsim 10^{9}\ \rm M_{\odot}$) are the major ($\gtrsim 90$%) hosts for potential Pop III star formation at $z\lesssim 6$, where dense pockets of metal-poor gas may survive to form Pop III stars, under inefficient mixing of metals released by supernovae. Metal mixing is the key process that determines not only when Pop III star formation ends, but also the total mass, $M_{\rm PopIII}$, of \textit{active} Pop III stars per host halo, which is a crucial parameter for direct detection and identification of Pop III hosts. Both aspects are still uncertain due to our limited knowledge of metal mixing during structure formation. Current predictions range from early termination at the end of reionization ($z\sim 5$) to continuous Pop III star formation extended to $z=0$ at a non-negligible rate $\sim 10^{-7}\ \rm M_{\odot}\ yr^{-1}\ Mpc^{-3}$, with $M_{\rm PopIII}\sim 10^{3}-10^{6}\ \rm M_{\odot}$. This leads to a broad range of redshift limits for direct detection of Pop III hosts, $z_{\rm PopIII}\sim 0.5-12.5$, with detection rates $\lesssim 0.1-20\ \rm arcmin^{-2}$, for current and future space telescopes (e.g. HST, WFIRST and JWST). Our model also predicts that the majority ($\gtrsim 90$%) of the cosmic volume is occupied by metal-free gas. Measuring the volume filling fractions of this metal-free phase can constrain metal mixing parameters and Pop III star formation.

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