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Truly massive galaxy clusters play a pivotal role for a wealth of extragalactic and cosmological research topics comma and SNAPshot observations are ideally suited to identify the most promising targets for further comma in-depth cluster studies. The power of this approach was demonstrated by ACS-WFC3 SNAPshots of X-ray selected MACS and eMACS clusters (at z>0.3 and z>0.5 comma respectively) obtained in previous Cycles. Based on these data comma the CLASH MCT comma Hubble Frontier Fields comma and RELICS legacy programs selected 60% of their targets from these surveys. We propose to build upon the (e)MACS legacy SNAPshot programs by extending the surveyed redshift range to z=0.2 to create a volume-complete sample of highly X-ray luminous clusters at z=0.2-0.5. Our project will comma for the first time comma systematically explore the most massive clusters in the hugely promising z=0.2-0.3 range comma which already gave us some of the most extreme clusters and cluster lenses known comma e.g. comma the Bullet Cluster comma A1703 comma RXJ1347-11 comma and PLCK G171.9-40.7. By exploiting this barely tapped comma rich resource comma the proposed program will (a) identify yet more powerful gravitational telescopes for the next generation of in-depth studies of the distant Universe with HST and JWST comma (b) provide tight constraints on the mass distribution within these extreme systems comma (c) advance our understanding of the evolution and interactions of dark and luminous matter in cluster cores comma and (d) unveil Balmer Break Galaxies at zvirgul2 and Lyman-break galaxies at z>6 as F814W dropouts. Acknowledging broad community interest we waive our data rights for these observations.

真正庞大的星系团在众多河外天文学与宇宙学研究课题中扮演着关键角色，而快照观测（SNAPshot observations）是识别最具潜力目标以开展后续深入星系团研究的理想手段。这一方法的威力已通过前几期观测周期中获取的、针对X射线选MACS星系团（z>0.3）与eMACS星系团（z>0.5）的ACS-WFC3快照观测得到验证。基于这些数据，CLASH MCT、哈勃前沿场（Hubble Frontier Fields）及RELICS经典项目中60%的目标均选自这些巡天观测。我们提议在(e)MACS经典快照项目的基础上，将巡天红移范围扩展至z=0.2，以构建z=0.2-0.5区间内高X射线光度星系团的体积完备样本。本项目将首次系统探索极具潜力的z=0.2-0.3区间内的最庞大星系团——该区间已为我们带来若干已知最极端的星系团与星系团透镜，例如子弹头星系团（Bullet Cluster）、A1703、RXJ1347-11及PLCK G171.9-40.7。通过利用这一尚未充分开发的丰富资源，拟议项目将（a）为下一代利用哈勃太空望远镜（Hubble Space Telescope，HST）与詹姆斯·韦伯太空望远镜（James Webb Space Telescope，JWST）开展的遥远宇宙深度研究识别更多强大的引力透镜；（b）为这些极端系统内部的质量分布提供严格约束；（c）深化我们对星系团核心区暗物质与发光物质演化及相互作用的理解；（d）揭示z≈2的巴尔末断裂星系（Balmer Break Galaxies）与z>6的莱曼断裂星系（Lyman-break galaxies）作为F814W缺失星系的存在。鉴于广泛的社区兴趣，我们放弃这些观测数据的使用权。