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arXiv 2603.04872astro-ph.GAastro-ph.COastro-ph.SR
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宇宙年龄与球状星团 IV：多星族Population

The Age of the Universe with Globular Clusters IV: Multiple Stellar Populations

Berkeley Center for Cosmological Physics and Department of Physics, University of California, Berkeley（加州大学伯克利分校）；ICC, University of Barcelona（巴塞罗那大学）；ICREA（加泰罗尼亚高级研究学院）；Dipartimento di Fisica e Astronomia “Augusto Righi Università di Bologna（博洛尼亚大学）；INAF - Osservatorio di Astrofisica e Scienza dello Spazio di Bologna（意大利国家天体物理研究所波洛尼亚天文与空间科学观测站）；Lawrence Berkeley National Lab（劳伦斯伯克利国家实验室）

David Valcin, Raul Jimenez, Carmela Lardo, Uroš Seljak, Licia Verde

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AI总结：

通过分析球状星团的多星族Population，研究发现宇宙年龄为13.81±0.25Gyr，同时测量了金属含量和氦含量。

摘要：

我们重新审视通过银河系球状星团确定宇宙年龄的方法，通过明确考虑每个星团内部存在多个星族，扩展了之前的分析。使用高质量的哈勃空间望远镜颜色-亮度图，对69个球状星团进行分析，我们放松了标准单星族假设，并建模了两个具有独立年龄、金属含量、氦含量和人口比例的星族。推断过程使用了完整的颜色-亮度图形态，明确处理了场污染，并采用了一种分层框架，将非高斯年龄后验传播。允许多星族的存在对球状星团年龄估计几乎没有影响。最老星族的年龄仍与单星族假设下的结果完全一致，差异在0.6σ水平上。限制到金属含量较低的子样本（[Fe/H] < -1.5），我们推断出一个主导的古老成分，其平均年龄为t_GC=13.61±0.25(stat)±0.23(sys)Gyr。采用保守的大爆炸与第一个球状星团形成之间的延迟时间，我们得到宇宙年龄为t_U=13.81±0.25(stat)±0.23(sys)Gyr。除了年龄约束外，我们的分析还同时测量了不同星族的金属含量和氦含量，包括关于氦富集和人口比例的约束，这些结果与文献中独立的确定结果一致。这些结果表明，基于球状星团的宇宙时钟对恒星人口复杂性具有鲁棒性，强化了其作为精确且主要宇宙学模型无关的宇宙年龄探测器的作用。

英文摘要：

We revisit the determination of the age of the Universe from galactic globular clusters, extending previous analyses by explicitly accounting for the presence of multiple stellar populations within each cluster. Using high--quality \textit{Hubble Space Telescope} color--magnitude diagrams for 69 globular clusters, we relax the standard single--population assumption, and model two stellar populations with independent ages, metallicities, helium abundances, and population fractions. The inference is performed using the full color--magnitude diagram morphology, an explicit treatment of field contamination, and a hierarchical framework that propagates non--Gaussian age posteriors. Allowing for multiple stellar populations has a negligible impact on globular cluster age estimates. The ages of the oldest populations remain fully consistent with those obtained under the single--population assumption, with differences at the $0.6σ$ level. Restricting to the metal--poor subsample ([Fe/H] $< -1.5$), we infer a dominant old component with mean age $t_{\rm GC}=13.61\pm0.25\,\mathrm{(stat)}\,\pm0.23 \mathrm{(sys)}\,\mathrm{Gyr}$. Adopting a conservative delay between the Big Bang and the formation of the first globular clusters, we obtain an age of the Universe of $t_{\rm U}=13.81\pm0.25\,\mathrm{(stat)}\,\pm0.23 \mathrm{(sys)}\,\mathrm{Gyr}$. In addition to age constraints, our analysis yields simultaneous measurements of metallicity and helium content for the different populations, including constraints on helium enrichment and population fractions which are consistent with independent determinations from the literature. These results demonstrate that globular--cluster--based cosmic chronometry is robust to stellar population complexity, reinforcing its role as a precise and largely cosmological model--independent probe of the age of the Universe.

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