AI 中文总结
本研究通过多代码多参数分析，发现依赖金属丰度的恒星形成率框架下的双黑洞种群合成模型普遍高估局域双黑洞并合率，提出需采用更强诞生踢或非标准质量转移等模型缓解张力。
AI 中文摘要
近期研究表明，结合基于观测的、依赖金属丰度的恒星形成率密度的双黑洞种群合成模型，会高估观测到的局域双黑洞（BBH）并合率密度。这种张力的显著性可能因所采用的具体代码和参数而异，因此需要对参数空间进行更广泛的探索。本研究通过考虑来自多个种群合成代码的BBH并合效率，涵盖广泛的物理假设和参数选择，开展了此类扩展分析。我们采用受观测启发的金属丰度分布，探索了多种变体以包含观测不确定性。研究发现，这种张力依然存在：在我们的几乎所有金属丰度变体中（18种里的14种），所考虑的模型均未预测出处于观测90%可信区间内或低于该区间的局域BBH并合率；即便在4种最有利的金属丰度变体中，也仅有≤10%的模型与观测约束一致。我们表明，这种差异源于低质量星系和星暴贡献的低金属丰度尾端，以及在推导金属丰度分布时使用铁丰度而非氧丰度。即便那些预测中等BBH并合率的文献模型，在结合受观测启发的金属丰度分布时，也会向更高的并合率偏移。尽管未涵盖所有文献模型，但本分析显示，具有更强 natal kicks（ natal kicks 指诞生踢速度）和/或对质量转移及共包层物理的非标准处理的模型，是缓解与观测局域BBH并合率张力的最有前景途径。
英文摘要
Recent studies have suggested that binary population synthesis models, when coupled with observationally based, metallicity-dependent star formation rate density, overpredict the observed local binary black hole (BBH) merger rate density. The significance of this tension might vary depending on the specific code and parameters adopted. Thus, a more extensive exploration of the parameter space is required. In this work, we perform such an extended analysis by considering BBH merger efficiencies coming from multiple population synthesis codes across a wide range of physical assumptions and parameter's choices. We adopt an observationally motivated metallicity distribution, exploring several variations to encompass observational uncertainties. We find that the tension persists: in almost all our metallicity variations, 14 out of 18, none of the models considered predicts a local BBH merger rate within or below the observed $90\%$ credible interval. Even in the four most favorable metallicity variations, only $\lesssim 10\%$ of the models are consistent with the observational constraints. We show that such a discrepancy originates from the low-metallicity tail contributed by low-mass galaxies and starbursts, as well as from the use of iron abundance rather than oxygen abundance in deriving the metallicity distribution. Even literature models that predict moderate BBH merger rates shift toward higher merger rates when combined with observationally motivated metallicity distributions. Although not comprehensive of all the literature models, our analysis suggests that models featuring stronger natal kicks and/or non-standard treatments of mass-transfer and common-envelope physics provide the most promising avenue for alleviating the tension with the observed local BBH merger rate.
Comments8 pages, 7 figures
