超致密矮星系中大质量黑洞的形成：N体模拟中原始中等质量黑洞的迁移
Formation of massive black holes in ultra-compact dwarf galaxies: migration of primordial intermediate-mass black holes in N-body simulation
摘要：
最近对超致密矮星系（UCD）的观测研究发现，在其中心区域存在质量超过${10^6~\rm M_\odot}$的大质量黑洞（MBH）。在这里，我们认为这些MBH可以通过合并的中等质量黑洞（IMBH），质量为${[10^3-10^5]~{\rm M}_{\odot}}$，在矮星系的恒星核，这是UCD的祖先。我们用数值方法研究了这种形成过程的广泛的模型参数，使用N体模拟。这意味着IMBH的增长和反馈在本研究中被忽略。我们发现在大多数矮星模型中，只有大质量的$10^5~\rm M_\odot$的IMBH沉入其宿主矮星（$\approx 10^{10}~\rm M_\odot$）的中心区域，被其恒星核引力捕获在小于1 Gyr的范围内。我们还发现，较轻的IMBH与$[1 - 30] \times 10^3~\rm M_\odot$下沉到中心的低质量矮星（$\approx 10^{9}~\rm M_\odot$）由于更有效的动力学摩擦（DF）。此外，我们表明，IMBHs可以在中心形成双星，很少，在它们到达中心之前，这可能导致IMBHs合并，从而发射出可以被LISA检测到的引力波。最后，我们讨论了在UCD中形成MBH所需的IMBH数目以及恒星核在IMBH双星和合并中的物理作用。
英文摘要：
Recent observational studies of ultra-compact dwarf galaxies (UCDs) have discovered massive black holes (MBHs) with masses of more than ${10^6~\rm M_\odot}$, in their central regions. We here consider that these MBHs can be formed through merging of intermediate-mass black holes (IMBH), with masses of ${[10^3-10^5]~{\rm M}_{\odot}}$, within the stellar nuclei of dwarf galaxies, which are progenitors of UCDs. We numerically investigate this formation process for a wide range of model parameters using N-body simulations. This means that IMBH growth and feedback is neglected in this study. We find that only massive IMBHs of $10^5~\rm M_\odot$ sink into the central regions of their host dwarf ($\approx 10^{10}~\rm M_\odot$) to be gravitationally trapped by its stellar nucleus within less than 1 Gyr in most dwarf models. We also find that lighter IMBHs with $[1 - 30] \times 10^3~\rm M_\odot$ sink into the centre in low-mass dwarfs ($\approx 10^{9}~\rm M_\odot$) due to more efficient dynamical friction (DF). Additionally, we show that the IMBHs can form binaries in the centre and, rarely, before they reach the centre, which may lead to the IMBHs merging and thus emitting gravitational waves that could be detected by LISA. Finally, we discuss the required number of IMBHs for the MBH formation in UCDs and the physical roles of stellar nuclei in IMBH binaries and mergers.
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