Signatures of hierarchical mergers in black hole spin and mass distribution
Signatures of hierarchical mergers in black hole spin and mass distribution
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DOI：
10.1093/mnras/stab2315
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发表时间：
2021-04
影响因子：
4.8
通讯作者：
H. Tagawa;Z. Haiman;I. Bartos;B. Kocsis;K. Omukai
中科院分区：
文献类型：
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作者：
H. Tagawa;Z. Haiman;I. Bartos;B. Kocsis;K. Omukai
LIGO/Virgo 最近的引力波 (GW) 观测显示了分级合并的证据，其中合并的黑洞是先前黑洞合并事件的残余物。这些事件可能携带有关引力波源的天体物理宿主环境的重要线索。在本文中，我们提出了分层合并中预期的有效自旋参数（χeff）、进动自旋参数（χp）和线性调频质量（mchirp）的分布。在广泛的假设下，分层合并产生 (i) 合并二进制文件的典型总自旋平均值的单调增加，我们用 $\scriptstyle{{\bar{\chi }}_\mathrm{typ}\equiv \overline{(\chi _\mathrm{eff}^2+\chi _\mathrm{p}^2)^{1/2}}}$，大致达到第一代 (1g) BH 中的最大 mchirp，并且 (ii) 在较高 mchirp 时达到 ${\bar{\chi }}_\mathrm{typ}\sim 0.6$ 的稳定状态。我们建议 1g BH 的最大质量和典型自旋幅度可以根据 ${\bar{\chi }}_\mathrm{typ}$ 作为 mchirp 的函数来估计。在 LIGO/Virgo O1–O3a 中观察到的引力波数据倾向于在低 mchirp 时 ${\bar{\chi }}_\mathrm{typ}$ 增加，这与以~2σ 置信度分层合并导致 BH 自旋幅度的增长一致。使用 χeff、χp 和 mchirp 分布的贝叶斯分析表明，如果大多数合并是高代 BH（不在 1g-1g BH 之间），则 1g BH 的最大质量为 ∼15–$30\, {\rm M}_\odot$，这与活动星系核盘和/或核星团中的合并一致， 而如果合并主要源自球状星团，则 1g BH 倾向于具有~0.3 的非零自旋幅度。我们还预测，一旦 GW 事件数量增加到 ≳ O(100)，${\bar{\chi }}_\mathrm{typ}$ 分布中的分层合并的签名就可以自信地恢复。
Recent gravitational wave (GW) observations by LIGO/Virgo show evidence for hierarchical mergers, where the merging BHs are the remnants of previous BH merger events. These events may carry important clues about the astrophysical host environments of the GW sources. In this paper, we present the distributions of the effective spin parameter (χeff), the precession spin parameter (χp), and the chirp mass (mchirp) expected in hierarchical mergers. Under a wide range of assumptions, hierarchical mergers produce (i) a monotonic increase of the average of the typical total spin for merging binaries, which we characterize with $\scriptstyle{{\bar{\chi }}_\mathrm{typ}\equiv \overline{(\chi _\mathrm{eff}^2+\chi _\mathrm{p}^2)^{1/2}}}$, up to roughly the maximum mchirp among first-generation (1g) BHs, and (ii) a plateau at ${\bar{\chi }}_\mathrm{typ}\sim 0.6$ at higher mchirp. We suggest that the maximum mass and typical spin magnitudes for 1g BHs can be estimated from ${\bar{\chi }}_\mathrm{typ}$ as a function of mchirp. The GW data observed in LIGO/Virgo O1–O3a prefers an increase in ${\bar{\chi }}_\mathrm{typ}$ at low mchirp, which is consistent with the growth of the BH spin magnitude by hierarchical mergers at ∼2σ confidence. A Bayesian analysis using the χeff, χp, and mchirp distributions suggests that 1g BHs have the maximum mass of ∼15–$30\, {\rm M}_\odot$ if the majority of mergers are of high-generation BHs (not among 1g–1g BHs), which is consistent with mergers in active galactic nucleus discs and/or nuclear star clusters, while if mergers mainly originate from globular clusters, 1g BHs are favoured to have non-zero spin magnitudes of ∼0.3. We also forecast that signatures for hierarchical mergers in the ${\bar{\chi }}_\mathrm{typ}$ distribution can be confidently recovered once the number of GW events increases to ≳ O(100).