Hierarchical black hole mergers in young, globular and nuclear star clusters: the effect of metallicity, spin and cluster properties
Michela Mapelli, Marco Dall'Amico, Yann Bouffanais, Nicola Giacobbo, Manuel Arca Sedda, M. Celeste Artale, Alessandro Ballone, Ugo N. Di Carlo, Giuliano Iorio, … 展开作者
Michela Mapelli, Marco Dall'Amico, Yann Bouffanais, Nicola Giacobbo, Manuel Arca Sedda, M. Celeste Artale, Alessandro Ballone, Ugo N. Di Carlo, Giuliano Iorio, Filippo Santoliquido, Stefano Torniamenti
备注：
20 pages, 13 figures, accepted for publication in MNRAS
我们探讨层次黑洞（BH）合并在核星团（NSC），球状星团（GC）和年轻星团（YSC），占原始和动态组装的二进制黑洞（BBH）。我们发现，第一代和第n代动力学合并的中位质量是较大的GC和YSC相对于NSC，因为较轻的BH从较低质量的集群超新星踢弹出。此外，第一代和第n代黑洞的质量受到祖星金属丰度的强烈影响：在贫金属（富金属）的NSC中，第n代合并的初级黑洞的质量中值为$\sim{}24-38$ M $_\odot$（$\sim{}9-15$ M $_\odot$）。BH的最大质量主要取决于逃逸速度：在NSC中形成质量高达几千M $_\odot$的BH，而YSC和GC宿主质量高达几百M $_\odot$的BH。此外，我们计算的合并与至少一个组件中的对不稳定的质量间隙（$f_{\rm PI}$）和中等质量BH制度（$f_{\rm IMBH}$）的分数。在具有金属性$Z=0.002$的动力学BBH的基准模型中，我们分别在NSC、GC和YSC中发现了$f_{\rm PI}\approx{}0.05$、$0.02$和$0.007$（$f_{\rm IMBH}\approx{}0.01$、$0.002$和$0.001$）。$f_{\rm PI}$和$f_{\rm IMBH}$都在太阳金属丰度时下降至少一个数量级。最后，我们研究了GW190521的形成，假设它是一个几乎等质量的BBH或中间质量比inspiral。
英文摘要：
We explore hierarchical black hole (BH) mergers in nuclear star clusters (NSCs), globular clusters (GCs) and young star clusters (YSCs), accounting for both original and dynamically assembled binary BHs (BBHs). We find that the median mass of both first- and nth-generation dynamical mergers is larger in GCs and YSCs with respect to NSCs, because the lighter BHs are ejected by supernova kicks from the lower-mass clusters. Also, first- and nth-generation BH masses are strongly affected by the metallicity of the progenitor stars: the median mass of the primary BH of a nth-generation merger is $\sim{}24-38$ M$_\odot$ ($\sim{}9-15$ M$_\odot$) in metal-poor (metal-rich) NSCs. The maximum BH mass mainly depends on the escape velocity: BHs with mass up to several thousand M$_\odot$ form in NSCs, while YSCs and GCs host BHs with mass up to several hundred M$_\odot$. Furthermore, we calculate the fraction of mergers with at least one component in the pair-instability mass gap ($f_{\rm PI}$) and in the intermediate-mass BH regime ($f_{\rm IMBH}$). In the fiducial model for dynamical BBHs with metallicity $Z=0.002$, we find $f_{\rm PI}\approx{}0.05$, $0.02$ and $0.007$ ($f_{\rm IMBH}\approx{}0.01$, $0.002$ and $0.001$) in NSCs, GCs and YSCs, respectively. Both $f_{\rm PI}$ and $f_{\rm IMBH}$ drop by at least one order of magnitude at solar metallicity. Finally, we investigate the formation of GW190521 by assuming that it is either a nearly equal-mass BBH or an intermediate-mass ratio inspiral.
Mass and rate of hierarchical black hole mergers in young, globular and nuclear star clusters
分级合并是双黑洞形成的一个显著特征。在这里，我们提出了一个快速的半解析方法来模拟核星团（NSC），球状星团（GC）和年轻星团（YSC）的层次合并。由于逃逸速度的不同，神经干细胞中的层级合并比GC和YSC中的层级合并更常见。分级BBH的质量分布强烈地依赖于第一代BBH的性质，例如它们的祖先的金属丰度。在我们的基准模型中，我们在NSC中形成质量高达$\sim{}10^3$ M $_\odot$的黑洞（BH），在GC和YSC中形成质量高达$\sim{}10^2$ M $_\odot$的黑洞。当逃逸速度超过100 km~s $^{-1}$时，NSC中允许形成质量为$>10^3$ M $_\odot$的黑洞.等级合并导致的对不稳定的质量间隙和中等质量的黑洞的形成，但只在贫金属的环境。在我们的模型中，局部BBH合并率范围为$\sim{}10$至$\sim{} 60$ Gpc $^{-3}$ yr $^{-1}$ ;神经干细胞中的分级BBH占$\sim{}10^{-2}- 0.2$ Gpc $^{-3}$ yr $^{-1}$，具有$\sim{}10$ Gpc $^{-3}$ yr $^{-1}$的强上限。当我们的模型与第二个引力波瞬态目录比较时，我们发现多个形成通道有利于重现所观察到的BBH人口。
