THE ASSEMBLY OF SUPERMASSIVE BLACK HOLES AT HIGH REDSHIFTS
THE ASSEMBLY OF SUPERMASSIVE BLACK HOLES AT HIGH REDSHIFTS
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DOI：
10.1088/0004-637x/696/2/1798
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发表时间：
2008-07
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影响因子：
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通讯作者：
Takamitsu L. Tanaka;Z. Haiman
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文献类型：
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作者：
Takamitsu L. Tanaka;Z. Haiman
超大质量黑洞（SMBHs）的质量足以（≥×109 M☉）为斯隆数字巡天（SDSS）观测到的明亮红移z≈6类星体提供动力，被认为是由质量较小的“种子”黑洞合并和/或气体吸积而形成的。如果种子是来自第一代恒星的~ 102 M☉残余黑洞，它们必须在红移z = 6之前到位，并且必须避免在与其他黑洞合并时受到引力辐射引起的后坐力的巨大（×102 km s−1）踢出它们的母原星系。我们利用暗物质晕合并树模拟了红移z >.6处的SMBH质量函数，并结合了成长中的黑洞的晕占比、吸积历史和径向反冲轨迹的处方。我们的目的是：(1)通过探索广泛的参数空间区域，绘制出z≈6类星体黑洞成功组装的合理场景，以及(2)预测激光干涉仪空间天线（LISA）在每种场景下可探测到的低频引力波事件的速率。我们的主要发现如下：(1)~ 100 M☉种子黑洞可以在没有超爱丁顿吸积的情况下成长为SDSS类星体黑洞，但前提是它们必须在z≤30的小光晕中形成，并且随后吸积的时间≤60%；(2)在解释SDSS类星体黑洞所需的乐观假设的情况下，除非种子停止形成，或以严重减少的速率或占空比（例如，由于反馈）在z≤20-30，否则较低质量（×105 M☉> Mbh > few × 107 M☉）黑洞的质量密度会超过102-103倍。我们还提出了几个成功的组装模型及其LISA检测率，包括一个“最大”模型，该模型给出了最高的检测率（在z = 6时为~ 30 yr−1），而不会产生过多的SMBH总密度。
The supermassive black holes (SMBHs) massive enough (≳ few ×109 M☉) to power the bright redshift z ≈ 6 quasars observed in the Sloan Digital Sky Survey (SDSS) are thought to have assembled by mergers and/or gas accretion from less massive “seed” BHs. If the seeds are the ∼102 M☉ remnant BHs from the first generation of stars, they must be in place well before redshift z = 6, and must avoid being ejected from their parent protogalaxies by the large (several ×102 km s−1) kicks they suffer from gravitational-radiation-induced recoil during mergers with other BHs. We simulate the SMBH mass function at redshift z > 6 using dark matter halo merger trees, coupled with a prescription for the halo occupation fraction, accretion histories, and radial recoil trajectories of the growing BHs. Our purpose is (1) to map out plausible scenarios for successful assembly of the z ≈ 6 quasar BHs by exploring a wide region of parameter space, and (2) to predict the rate of low-frequency gravitational wave events detectable by the Laser Interferometer Space Antenna (LISA) for each such scenario. Our main findings are as follows: (1) ∼100 M☉ seed BHs can grow into the SDSS quasar BHs without super-Eddington accretion, but only if they form in minihalos at z ≳ 30 and subsequently accrete ≳60% of the time; (2) the scenarios with optimistic assumptions required to explain the SDSS quasar BHs overproduce the mass density in lower mass (few ×105 M☉ ≲ Mbh≲ few × 107 M☉) BHs by a factor of 102–103, unless seeds stop forming, or accrete at a severely diminished rates or duty cycles (e.g., due to feedback), at z ≲ 20–30. We also present several successful assembly models and their LISA detection rates, including a “maximal” model that gives the highest rate (∼30 yr−1 at z = 6) without overproducing the total SMBH density.