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arXiv 2008.01890astro-ph.HEastro-ph.SR
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在对不稳定质量隙之下、之上和之中的粒子数III二元黑洞的合并率密度

Merger rate density of Population III binary black holes below, above, and in the pair-instability mass gap

Ataru Tanikawa, Hajime Susa, Takashi Yoshida, Alessandro A. Trani, Tomoya Kinugawa

备注：
38 pages, 33 figures, accepted for publication in ApJ
发表信息：
The Astrophysical Journal, 910:30 (31pp), 2021 March
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摘要：

我们提出了人口合并率密度（Pop.）III二元黑洞（BH）的广泛使用的二元人口合成代码BSE扩展到非常大质量和极端贫金属的恒星。我们不仅考虑了低质量的BH（lBH：$5-50 M_\odot$），而且考虑了高质量的BH（hBH：$130-200 M_\odot$），其中lBH和hBH分别低于和高于对不稳定质量间隙（$50-130 M_\odot$）。人群III BH-BH可分为三个亚群：无hBH的BH-BH（hBH 0 s：$m_{\rm tot} \lesssim 100 M_\odot$）、有1个hBH的BH-BH（hBH 1 s：$m_{\rm tot} \sim 130-260 M_\odot$）和有2个hBH的BH-BH（hBH 2 s：$m_{\rm tot} \sim 270-400 M_\odot$），其中$m_{\rm tot}$是BH-BH的总质量。它们在当前宇宙中的合并率密度对于hBH 0是$\sim 0.1$ yr $^{-1}$ Gpc $^{-3}$，对于hBH 1 s和hBH 2 s之和是$\sim 0.01$ yr $^{-1}$ Gpc $^{-3}$，前提是Pop. III恒星的质量密度是$\sim 10^{13} M_\odot$ Gpc $^{-3}$。这些速率对初始条件和单星模型不太敏感。hBH 1和hBH 2合并可能在不久的将来发现的hBH中占主导地位。它们在当前宇宙中具有低有效自旋$\lesssim 0.2$。hBH 2s与hBH 1 s的数量比很高，$\gtrsim 0.1$。我们还发现BH在质量间隙（高达$\sim 85 M_\odot$）合并。如果Pop. III双星总是宽的（$\gtrsim 100 R_\odot$），并且如果Pop. III恒星总是进入化学均匀演化，那么合并率可以降低到几乎为零。密切的Pop. III二进制文件（$\sim 10 R_\odot$）的存在对于避免最坏的情况至关重要。

英文摘要：

We present the merger rate density of Population (Pop.) III binary black holes (BHs) by means of a widely-used binary population synthesis code BSE with extensions to very massive and extreme metal-poor stars. We consider not only low-mass BHs (lBHs: $5-50 M_\odot$) but also high-mass BHs (hBHs: $130-200 M_\odot$), where lBHs and hBHs are below and above the pair-instability mass gap ($50-130 M_\odot$), respectively. Pop. III BH-BHs can be categorized into three subpopulations: BH-BHs without hBHs (hBH0s: $m_{\rm tot} \lesssim 100 M_\odot$), with one hBH (hBH1s: $m_{\rm tot} \sim 130-260 M_\odot$), and with two hBHs (hBH2s: $m_{\rm tot} \sim 270-400 M_\odot$), where $m_{\rm tot}$ is the total mass of a BH-BH. Their merger rate densities at the current universe are $\sim 0.1$ yr$^{-1}$ Gpc$^{-3}$ for hBH0s, and $\sim 0.01$ yr$^{-1}$ Gpc$^{-3}$ for the sum of hBH1s and hBH2s, provided that the mass density of Pop. III stars is $\sim 10^{13} M_\odot$ Gpc$^{-3}$. These rates are modestly insensitive to initial conditions and single star models. The hBH1 and hBH2 mergers can dominate BH-BHs with hBHs discovered in near future. They have low effective spins $\lesssim 0.2$ in the current universe. The number ratio of the hBH2s to the hBH1s is high, $\gtrsim 0.1$. We also find BHs in the mass gap (up to $\sim 85 M_\odot$) merge. These merger rates can be reduced to nearly zero if Pop. III binaries are always wide ($\gtrsim 100 R_\odot$), and if Pop. III stars always enter into chemically homogeneous evolution. The presence of close Pop. III binaries ($\sim 10 R_\odot$) are crucial for avoiding the worst scenario.

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