超大质量黑洞周围气体盘中恒星级质量相互作用黑洞的轨道迁移 III. 层级并合的质量分布
Orbital Migration of Interacting Stellar Mass Black Holes in Disks around Supermassive Black Holes. III. Mass Distribution of Hierarchical Mergers
AI总结：
本研究通过360次N体模拟发现，AGN气体盘的迁移陷阱区域可形成层级并合双黑洞，能解释LVK观测到的部分双黑洞并合，还会形成200倍太阳质量以上的中等质量黑洞，可用于约束AGN吸积盘模型。
AI中文摘要：
活动星系核（AGN）气体盘是形成双黑洞（BBH）的理想场所，这些双黑洞会在相对较短的时间尺度内并合，并被LIGO-Virgo-KAGRA（LVK）探测到。为了将AGN气体盘中经历层级并合的黑洞（BH）的质量函数（MF）与LVK观测推断出的质量函数进行比较，我们使用一种N体代码开展了360次模拟，该代码新增了迁移扭矩和其他气体力的解析模型。我们重点关注AGN气体盘中迁移陷阱周围的区域，此处迁移扭矩相互抵消，黑洞在此汇聚。我们发现，无论初始质量函数和双黑洞并合判据如何变化，频繁的并合都会使质量≤10倍太阳质量（M⊙）的黑洞数量减少，并在40-100倍太阳质量的上质量间隙中形成近似均匀的分布，其中因共振轨道天体导致约70倍太阳质量处存在轻微过量。我们还发现，在我们的AGN气体盘模型中，由迁移陷阱辅助形成的双黑洞并合的平均并合率约为6 Gpc⁻³ yr⁻¹，其中约40%的并合具有不等质量比，16%的并合主黑洞质量在50-100倍太阳质量范围内。因此，AGN气体盘很容易成为LVK观测到的、难以通过传统恒星演化通道产生的双黑洞并合的来源。我们的模拟还在约2百万年（Myr）后形成了一个独立的、质量大于200倍太阳质量的大质量中等质量黑洞（IMBH）种群，未来的引力波探测器可通过对该中等质量黑洞种群的观测来约束AGN吸积盘模型。
英文摘要：
Active galactic nucleus (AGN) disks are a promising location for the formation of binary black holes (BBHs) that will merge on relatively short timescales and be detected by LIGO-Virgo-KAGRA (LVK). To compare the mass function (MF) of black holes (BHs) undergoing hierarchical mergers in AGN disks to the inferred MFs from LVK observations, we perform 360 simulations with an N-body code augmented to include an analytic model for migration torques and other gas forces. We focus on the region surrounding migration traps in AGN disks where migration torques cancel out and BHs converge. We find that regardless of changes in the initial MF and BBH merger criteria, frequent mergers deplete the number of BHs with masses $\lesssim 10$~$M_\odot$ and fill the upper mass gap with a roughly uniform distribution from 40--100~$M_\odot$, with a slight overabundance around ${\approx}70~M_\odot$ from resonant orbiters. We also find an average merger rate of $\sim 6$~Gpc$^{-3}$~yr$^{-1}$ for migration-trap-aided BBH mergers in our AGN disk model. $\sim 40\%$ of these mergers have uneven mass ratios and 16\% have a primary mass $\in[50-100]~M_\odot$. Therefore, AGN disks could easily be the source of BBH mergers observed by LVK that are difficult to produce through traditional stellar evolution channels. Our simulations also form a separate higher-mass intermediate mass black hole (IMBH) population $>200~M_\odot$ after $\sim 2$~Myr. Future gravitational wave detectors can use observations of this IMBH population to constrain models of AGN accretion disks.
