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arXiv 0904.1383astro-ph.CO
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粘性波和引力波驱动的发光AGN中超大质量黑洞双星的布居

The Population of Viscosity- and Gravitational Wave-Driven Supermassive Black Hole Binaries Among Luminous AGN

Zoltán Haiman, Bence Kocsis, Kristen Menou

摘要:

星系核中的超大质量黑洞双星(SMBHB)被认为是主要星系合并的常见副产品。我们使用简单的磁盘模型的环双星气体和双星磁盘的相互作用,以遵循轨道衰变的SMBHB的总质量(M)和质量比(q)的范围内,通过物理上不同的区域的磁盘,直到引力波(GW)接管他们的演变。在GW驱动阶段之前,粘性衰减处于停滞的“次级主导”状态。SMBHB在轨道周期t_var介于1天和1年之间的时间里,花费了不可忽略的10^7年。专门的光学或X射线测量可以统计地识别合并的SMBHB,作为周期性变化的类星体的群体,其丰度N_var与t_var^alpha成比例,在大约几十周的周期t_var范围内。M < 10^7 M_sun,0.5 < alpha < 1.5的SMBHB将探测粘性轨道衰变的物理学,而检测到α =8/3的更高质量的双星,将证实它们的衰变是由GWs驱动的。最低质量的SMBHB(M < 10^{5-6} M_sun)在激光干涉空间天线(LISA)的频带内以短轨道周期进入GW驱动区。虽然粘性过程在过去几年的合并中是强烈的次主导,但它们可以减少近静止LISA源的任何未解决背景的振幅。我们讨论了从现有数据中获得的SMBHB人口的限制,以及在未来调查中检测的灵敏度和天空覆盖要求。SMBHBs也可以确定其光谱中的速度变化,我们讨论了预期的丰富SMBHBs作为其轨道速度的函数。

英文摘要:

Supermassive black hole binaries (SMBHBs) in galactic nuclei are thought to be a common by-product of major galaxy mergers. We use simple disk models for the circumbinary gas and for the binary-disk interaction to follow the orbital decay of SMBHBs with a range of total masses (M) and mass ratios (q), through physically distinct regions of the disk, until gravitational waves (GWs) take over their evolution. Prior to the GW-driven phase, the viscous decay is in the stalled "secondary-dominated" regime. SMBHBs spend a non-negligible fraction of 10^7 years at orbital periods t_var between a day and a year. A dedicated optical or X-ray survey could identify coalescing SMBHBs statistically, as a population of periodically variable quasars, whose abundance N_var is proportional to t_var^alpha, in a range of periods t_var around tens of weeks. SMBHBs with M < 10^7 M_sun, with 0.5 < alpha < 1.5, would probe the physics of viscous orbital decay, whereas the detection of a population of higher-mass binaries, with alpha=8/3, would confirm that their decay is driven by GWs. The lowest mass SMBHBs (M < 10^{5-6} M_sun) enter the GW-driven regime at short orbital periods, in the frequency band of the Laser Interferometric Space Antenna (LISA). While viscous processes are strongly sub-dominant in the last few years of coalescence, they could reduce the amplitude of any unresolved background of near-stationary LISA sources. We discuss constraints on the SMBHB population available from existing data, and the sensitivity and sky coverage requirements for a detection in future surveys. SMBHBs may also be identified from velocity shifts in their spectra; we discuss the expected abundance of SMBHBs as a function of their orbital velocity.

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