红移 z∼2 的第三族星候选体：HETDEX Lyα 发射体中强 He II λ1640 且无紫外金属线
Population III Host Candidates at $z\sim2$: Strong He II $\lambda1640$ and Absent UV Metal Lines in HETDEX Ly$α$ Emitters
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中文总结 AI 辅助
在HETDEX数据中搜索z~2的Lyα发射星系，发现8个具有强He II且无紫外金属线的候选体，可能是极贫金属或第三族星电离源，数密度约30 Gpc⁻³。
中文摘要 AI 辅助
第三族星（Pop III）预计会产生极其硬化的电离光谱，然而其标志性特征——强窄 He II λ1640 发射且金属线弱或缺失——的直接证据仍然难以捉摸。尽管第三族星的形成在 z≳10 时达到峰值，但模型预测近乎原始的气体口袋可以存活到更晚的时期，这使得中等红移搜索成为探测宇宙时间尺度上金属混合的探针。我们在霍比-埃伯利望远镜暗能量实验（HETDEX）数据库中搜索了 109,545 个高置信度 Lyα 发射星系（1.9<z<2.3），寻找具有强 He II λ1640 且未探测到紫外金属线的系统，恢复了八个候选体，并得到一阶的、暂定的共动数密度约为 30 Gpc⁻³。这八个天体的叠加谱给出了静止系 He II 等值宽度为 28.7±6.7 埃，He II/Lyα=0.354±0.094，以及分辨率校正后的 He II 半高全宽（FWHM）为 449±105 km s⁻¹。我们未发现显著的 N V、C IV 或 O III] 发射；以 He II 宽度为尺度，我们推导出 N V/He II <0.167、C IV/He II <0.128 和 O III]/He II <0.140 的 3σ 上限。这种强 He II、升高的 He II/Lyα、中等线宽和弱金属线的组合难以用富金属恒星族、活动星系核（AGN）窄线区、激波或经典沃尔夫-拉叶星特征来重现。我们将该样本解释为 z∼2 处极贫金属或类第三族星电离源的候选体。最终确认需要更深的静止系紫外光谱来测量单个天体中的 He II 和金属线上限，随后进行 Hβ、[O III] λ4959,λ5007、[O II] λ3727 和 Hα 的静止系光学光谱观测，以约束气相金属丰度、电离条件和 AGN 活动。
英文摘要
Population III (Pop III) stars are expected to produce extremely hard ionizing spectra, yet direct evidence for their signature--strong narrow He II $\lambda1640$ emission with weak or absent metal lines--remains elusive. Although Pop III formation peaks at $z\gtrsim10$, models predict that nearly pristine gas pockets can survive to later times, making intermediate-redshift searches a probe of metal mixing across cosmic time. We search 109,545 high-confidence Ly$α$-emitting galaxies at $1.9<z<2.3$ in the Hobby--Eberly Telescope Dark Energy Experiment's database for systems with strong He II $\lambda1640$ and no detected UV metal lines, recovering eight candidates and a first-order, tentative comoving number density of $\sim30$ Gpc$^{-3}$. The eight-object stack yields a rest-frame He II equivalent width of $28.7\pm6.7$ Angstrom, He II/Ly$α=0.354\pm0.094$, and a resolution-corrected He II FWHM of $449\pm105$ km s$^{-1}$. We find no significant N V, C IV, or O III] emission; using the He II width to set the scale, we derive $3σ$ upper limits of N V/He II $<0.167$, C IV/He II $<0.128$, and O III]/He II $<0.140$. This combination of strong He II, elevated He II/Ly$α$, moderate line width, and weak metal lines is difficult to reproduce with metal-enriched stellar populations, AGN narrow-line regions, shocks, or classical Wolf--Rayet features. We interpret the sample as candidates for very metal-poor or Pop III-like ionizing sources at $z\sim2$. Definitive confirmation requires deeper rest-UV spectroscopy to measure He II and metal-line limits in individual objects, followed by rest-optical spectroscopy of H$β$, [O III] $\lambda4959,\lambda5007$, [O II] $\lambda3727$, and H$α$ to constrain gas-phase metallicity, ionization conditions, and AGN activity.
发表机构
- The University of Texas at Austin（德克萨斯大学奥斯汀分校）
- Cosmic Frontier Center, The University of Texas at Austin（德克萨斯大学奥斯汀分校宇宙前沿中心）
机构由 AI 辅助整理，请以论文原文为准。
