Gravitational Wave Backgrounds from Coalescing Black Hole Binaries at Cosmic Dawn: An Upper Bound
Gravitational Wave Backgrounds from Coalescing Black Hole Binaries at Cosmic Dawn: An Upper Bound
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DOI：
10.3847/1538-4357/ac106d
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发表时间：
2021-03
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影响因子：
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通讯作者：
K. Inayoshi;K. Kashiyama;E. Visbal;Z. Haiman
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文献类型：
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作者：
K. Inayoshi;K. Kashiyama;E. Visbal;Z. Haiman
高级LIGO-Virgo连续发现的双黑洞并合事件揭示了双黑洞（BBH）群体的统计特性。随机引力波背景（GWB）是探测这些紧密合并的宇宙演化的有用工具。在本文中，我们研究了由BBH合并产生的GWB的上界，这些合并的恒星祖先主导了宇宙黎明的再电离过程。由于这些前体的早期再电离产生了与普朗克测量结果不一致的高宇宙光学深度，累积质量密度被限制在ρ - - - 107 M⊙Mpc−3。在此上限下，在f≃25 Hz处，高z BBH合并导致的GWB振幅高达Ωgw≃1.48−1.27+1.80×10−9，而目前的合并率与观测到的GW事件率一致或更低。这种水平的GWB在Advanced LIGO-Virgo的设计灵敏度下可以检测到，这将表明高z BBH种群对当地GW事件的主要贡献。该光谱指数比一般由低红移和低质量BBHs产生的标准值大体上平坦。此外，如果它们的质量函数比本地宇宙更重，那么GWB频谱甚至更倾向于较低的频率，这将使我们能够在高红移处提取合并bbh的质量函数信息。
The successive discoveries of binary merger events by Advanced LIGO-Virgo have been revealing the statistical properties of binary black hole (BBH) populations. A stochastic gravitational wave background (GWB) is a useful tool to probe the cosmological evolution of those compact mergers. In this paper, we study the upper bound on a GWB produced by BBH mergers, whose stellar progenitors dominate the reionization process at the cosmic dawn. Since early reionization by those progenitors yields a high optical depth of the universe inconsistent with the Planck measurements, the cumulative mass density is limited to ρ ⋆ ≲ 107 M ⊙ Mpc−3. Even with this upper bound, the amplitude of a GWB owing to the high-z BBH mergers is expected to be as high as Ωgw≃1.48−1.27+1.80×10−9 at f ≃ 25 Hz, while their merger rate at the present day is consistent or lower than the observed GW event rate. This level of GWB is detectable at the design sensitivity of Advanced LIGO-Virgo and would indicate a major contribution of the high-z BBH population to the local GW events. The spectral index is expected to be substantially flatter than the canonical value of ≃2/3 generically produced by lower-redshift and less-massive BBHs. Moreover, if their mass function is more top heavy than in the local universe, the GWB spectrum is even more skewed toward lower frequencies, which would allow us to extract information on the mass function of merging BBHs at high redshifts.