发表机构
Instituto de Física de Cantabria (CSIC-UC); The University of Hong Kong; The Hong Kong Institute for Astronomy and Astrophysics, The University of Hong Kong; David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto（坎塔布里亚物理研究所; 香港大学; 香港大学香港天文与天体物理研究所; 多伦多大学戴维·A·邓普尔天文与天体物理系）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文提出在并合星系团的 pristine 区域观测第三星族恒星作为临界穿越事件，该区域微透镜密度低，可使放大率接近理论极限，从而用 JWST 约 29 星等观测直接探测单个 Pop III 恒星。
AI 中文摘要
探测长期寻找的第三星族（Pop III）恒星，或许是现代天文学中最引人入胜的缺失环节之一。临界穿越事件（CCE）——星系团临界曲线处对宇宙学距离上单个恒星产生的极端放大效应——被认为能够直接探测单个 Pop III 恒星。然而，在通常的 CCE 情形下，星系团内恒星作为微透镜的丰富存在限制了可达到的最大放大率，从而将明亮恒星的理论探测限制在相对较低的红移，远低于预期 Pop III 恒星存在的红移。在本信中，我们提出在并合星系团的 pristine 区域中观测 Pop III 恒星群作为 CCE。Pristine 区域定义为透镜中星系团内光（以及相应的恒星微透镜）异常低的区域。在这些区域中，微透镜的低密度使得背景恒星群能够达到更接近理论极限（无微透镜）的放大率。我们证明 pristine 区域中的最大放大率与恒星微透镜的表面质量密度成反比。采用 Pop III 等时线，常规的詹姆斯·韦布约 29 星等观测足以探测 pristine 区域中的单个 Pop III 恒星，为利用即将到来的星系团观测探测 Pop III 恒星提供了一种独特的观测策略。高红移并合星系团（如 El Gordo）之间的中间区域天然缺乏微透镜，构成搜寻 Pop III 恒星的绝佳目标。
英文摘要
The detection of the long-sought Population III (Pop III) stars is, perhaps, one of the most intriguing missing links in modern astronomy. Caustic crossing events (CCE) -- extreme magnification at the critical curves of galaxy clusters of individual stars at cosmological distances -- are postulated to allow for the direct detection of individual Pop III stars. However, in the usual CCE regime, the abundant existence of intracluster stars as microlenses limits the maximum magnification attainable, thus limiting the theoretical detection of luminous stars to relatively low redshifts, significantly smaller than the redshifts where Pop III stars are expected to exist. Here in this letter, we propose to observe Pop III stellar populations as CCEs in the pristine regions of merging clusters. Pristine regions are defined as areas in the lens where the intracluster light, and hence the corresponding stelalr microlenses, is exceptionally low. In thes regions, the low density of microlenses allows background stellar populations to achieve magnification closer to the theoretical limit (whitout microlenses). We show that the maximum magnification in the pristine region scales inversely with the surface mass density of stellar microlenses. Adopting Pop III isochrones, regular James-Webb $\sim29\,$mag observations are sufficient to detect individual Pop III stars in pristine regions, offering a unique observational strategy to detect Pop III stars with the incoming cluster observations. The intermediate regions between high-redshift merging clusters (such as El Gordo) are naturally devoid of microlenses and constitute exceptional targets for the search of Pop III stars.
Comments5 pages, 4 figures. To be submitted, comments welcomed
