发表机构
University of Missouri; Arizona State University; Università degli Studi di Milano; Uppsala University; The University of Western Australia（密苏里大学; 亚利桑那州立大学; 米兰大学; 乌普萨拉大学; 西澳大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
利用 MACS0416 星系团强透镜焦散的高放大效应，通过三次观测差分图像搜寻高红移 Pop III 恒星穿越事件，零结果将 100 太阳质量 Pop III 天区表面亮度约束至 >= 32.8 星等每平方角秒，并给出穿越率上限。
AI 中文摘要
第三族恒星（Pop III）是假设的零金属度恒星结构，由原初氢和氦形成。理论上它们跨越广泛的质量范围，可延伸至数百个太阳质量，并可能在核合成和再电离中发挥重要作用。它们的预期通量远低于 JWST NIRCam 的探测极限，使得直接观测不太可能。然而，大质量前景星系团焦散附近的极端放大可能使其得以探测。我们在透镜星系团 MACS J0416.1-2403 中搜寻被忽略的高红移（7 <= z <= 17）焦散穿越事件。利用跨越 126 天的三次观测，我们生成差分图像以识别潜在候选体。基于强透镜模型导出的 7 <= z <= 17 源的红移临界曲线，指导了对三幅差分图像的目视检查。未发现额外的穿越事件。我们模型中的较长焦散扫过更大的源平面面积，增加了探测事件的可能性。将这种增强的统计灵敏度与更深的成像相结合，我们为 z >= 7 处未分辨恒星族群设定了更暗的极限。基于这一零结果，我们将 100 太阳质量、2 微米波段的 Pop III 天区表面亮度约束为 >= 32.8 +/- 0.6 星等每平方角秒。将非探测建模为泊松过程，得到后验平均焦散穿越率为 0.29 星系团^-1 年^-1，95% 置信上限为 lambda_95 = 0.86 星系团^-1 年^-1。推断的速率与采用的基准 Pop III 焦散穿越模型保持一致，并为未来的多历元监测活动提供了经验基准。这项搜索利用了投影在源平面焦散附近的单颗恒星可被短暂放大至远超其未透镜通量的事实。这些约束为早期宇宙时期明亮 Pop III 恒星的丰度提供了直接检验。
英文摘要
Population III (Pop III) stars are hypothetical zero-metallicity stellar structures formed from primordial hydrogen and helium. They are theorized to span a wide mass range, extending to several 100 solar masses, and may have played important roles in nucleosynthesis and reionization. Their expected fluxes are far below JWST NIRCam detection limits, making direct observation unlikely. However, extreme magnification near the caustics of massive foreground galaxy clusters may enable their detection. We search for overlooked high-redshift (7 <= z <= 17) caustic transits in the lensing cluster MACS J0416.1-2403. Using three observations spanning 126 days, we create difference images to identify potential candidates. Critical curves for sources at 7 <= z <= 17, derived from a strong-lensing model, guided visual inspection of three difference-images. No additional transits were found. The longer caustics in our model sweep a larger source-plane area, increasing the probability of detecting an event. Combining this increased statistical sensitivity with deeper imaging, we establish a fainter limit for the unresolved stellar population at z >= 7. From this null result, we constrain the 100 solar mass 2 micron Pop III sky surface brightness to >= 32.8 +/- 0.6 mag arcsec^-2. Modeling the non-detection as a Poisson process gives a posterior mean caustic-transit rate of 0.29 cluster^-1 yr^-1 and a 95 percent upper credible limit of lambda_95 = 0.86 cluster^-1 yr^-1. The inferred rate remains consistent with the adopted fiducial Pop III caustic-transit model and provides an empirical benchmark for future multi-epoch monitoring campaigns. This search exploits the fact that individual stars projected close to source-plane caustics can be briefly magnified far beyond their unlensed fluxes. These constraints provide a direct test of the abundance of luminous Pop III stars at early cosmic times.
