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arXiv 2109.12129astro-ph.GA
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有核矮星系中中等质量黑洞双星的极有效合并

Extremely efficient mergers of intermediate mass black hole binaries in nucleated dwarf galaxies

Fazeel Mahmood Khan, Kelly Holley-Bockelmann

摘要:

由$\sim 10^4-10^7~M_\odot$之间的黑洞合并发出的引力波将被激光干涉仪空间天线(LISA)探测到,其信噪比高达几百到红移20。超大质量黑洞($10^7$ ~M $_{\odot}$ - $10^{10}$ ~M $_{\odot}$)双星在大质量星系中的形成、并合和合并过程已被广泛研究。然而,中低质量黑洞(IMBH)是由低质量和矮星系托管的;将黑洞合并的时间尺度外推到这个IMBH双星制度并不是微不足道的,因为与大质量星系宿主相比,宿主星系的结构,运动学和形态完全不同。我们进行超高分辨率的$N$体模拟来研究有核矮星系中的IMBH动力学,其结构参数是从附近矮星系的观测中获得的。从50秒差距开始,IMBH很快就形成了一个二进制。此后,由于核星团(NSC)提供的高中心恒星密度,双星轨道迅速收缩。我们发现高偏心率($e \sim 0.4-0.99$)在我们的套件的IMBH二进制文件,和剩余偏心率可能会持续到LISA制度。IMBH的合并时间通常是几亿年,有几个异常短的合并时间为高偏心率。我们发现,IMBH恒星的遭遇主要来自NSC,如果NSC-IMBH二进制质量比大于10,否则,凸起的恒星贡献显着。然而,作为IMBH双星,NSC被破坏了。我们的结论是,相当质量的IMBH合并非常有效的有核矮星系,使他们有前途的LISA源,以及IMBH增长的渠道。

英文摘要:

Gravitational waves emitted by merging black holes between $\sim 10^4-10^7~M_\odot$ will be detectable by the Laser Interferometer Space Antenna (LISA) with signal-to-noise ratios of several hundred out to redshift 20. Supermassive black hole ($10^7$~M$_{\odot}$ - $10^{10}$~M$_{\odot}$) binary formation, coalescence and merger within massive galaxies is well-studied. However, low-to-intermediate mass black holes (IMBHs) are hosted by low-mass and dwarf galaxies; it is not trivial to extrapolate black hole merger timescales to this IMBH binary regime, due to the starkly different host galaxy structure, kinematics, and morphology compared to massive galaxy hosts. We perform ultra-high resolution $N$-body simulations to study IMBH dynamics in nucleated dwarf galaxies whose structural parameters are obtained from observations of nearby dwarf galaxies. Starting from 50 parsecs, an IMBH quickly forms a binary. Thereafter, the binary orbit shrinks rapidly due to the high central stellar densities furnished by nuclear star clusters (NSCs). We find high eccentricities ($e \sim 0.4-0.99$) in our suite of IMBH binaries, and residual eccentricity may persist to the LISA regime. IMBH merger times are typically a few hundred million years, with a few exceptionally short merger times for high eccentricities. We find that IMBH-stellar encounters originate predominantly from NSCs, if the NSC-to-IMBH binary mass ratio is greater than 10; otherwise, bulge stars contribute significantly. As the IMBH binary ejects stars, however, the NSCs is disrupted. We conclude that comparable-mass IMBHs merge very efficiently in nucleated dwarf galaxies, making them promising LISA sources, as well as a channel for IMBH growth.

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