Metallicity Distributions of the Faintest Dwarf Galaxies

超暗矮星系（ufd）似乎是已知的最古老、暗物质占主导地位最严重、金属含量最低的星系。它们似乎在宇宙存在的最初10 - 20亿年里形成了所有的恒星。因此，它们的恒星群保留了早期工作过程的重要信息，包括第一代恒星（星族III）的形成和再电离。虽然高红移ufd太微弱，甚至连JWST都无法研究，但原则上，附近的例子应该能够提供足够的信息来重建它们的形成历史，并约束星系的形成。首席研究员（PI）和他的团队将使用麦哲伦望远镜获得的深度光谱和光度测定法，从附近四个ufd中的每一个中得出50-200颗主序关闭（MSTO）恒星的金属丰度，这是测量化学丰度的两倍多。对由此产生的金属丰度分布函数（MDFs）的分析有望为这些天体提供精确的恒星形成历史，从而为第一批星系的形成提供重要的约束。这项工作的一个令人兴奋的次要目标是有可能在观测到的MSTO恒星中探测到单个的III星族恒星并限制它们的质量函数。该奖项将支持研究生的培训，并为代表性不足的本科生提供研究经验。PI还将在夏季为本科生研究人员举办一系列讲座。研究人员将获得能够在每个目标UFD星系中对50- 200颗MSTO恒星进行金属丰度测量的深度光谱。这将产生迄今为止最大的金属丰度样品，用于这些系统的化学演化建模。该团队将打破基于等时线的恒星形成历史中的年龄-金属丰度简并，这将使单个msto的年龄精度达到千兆年以下。年龄和金属丰度将通过同时拟合恒星光度和线等效宽度来确定。这将导致对ufd形成历史的最佳测量，这将使数据成为化学演化或流体动力学星系形成模拟的宝贵测试。这些形成历史将通过展示在最微弱的矮星系中恒星形成停止的速度来推进对星系形成边缘的理解。考虑到极低的UFD恒星质量和大量的金属丰度测量，也有很大的机会发现一颗幸存的III星族恒星，这将是同类恒星中的第一颗。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Ultra-faint dwarf galaxies (UFDs) appear to be the oldest, the most dark matter dominated, and the most metal-poor galaxies known. They appear to have formed all of their stars during the universe’s first 1-2 billion years of existence. As such, their stellar populations retain important information concerning processes at work during this early epoch, including the formation of the first generation of stars (Population III) and reionization. While high redshift UFDs are too faint to be studied by even the JWST, nearby examples should in principle be capable of yielding enough information to reconstruct their formation history and constrain galaxy formation. The principal investigator (PI) and his team will use deep spectroscopy and photometry obtained with the Magellan telescope to derive metallicities of 50-200 Main-Sequence turn-off (MSTO) stars for each of four nearby UFDs, more than doubling the number with measured chemical abundances. Analysis of the resulting metallicity distribution functions (MDFs) promises to yield precise star formation histories for these objects and thus provide important constraints on the formation of the first galaxies. An exciting secondary goal of this work is the possibility of detecting individual Population III stars among the observed MSTO stars and constraining their mass function. This award will support the training of a graduate student as well as research experiences for underrepresented undergraduate students. The PI will also implement a series of talks during the summer for undergraduate researchers.The researchers will obtain deep spectroscopy capable of enabling metallicity measurements for 50- 200 MSTO stars in each of the targeted UFD galaxies. This will result in the largest metallicity sample to date for chemical evolution modeling of these systems. The team will break age-metallicity degeneracies in isochrone-based star formation histories, which will enable sub-gigayear age precision for individual MSTOs. Ages and metallicities will be determined by simultaneously fitting stellar photometry and line equivalent widths. These will lead to the best-measured formation histories of UFDs, which will make the data invaluable as tests of chemical evolution or hydrodynamic galaxy formation simulations. These formation histories will advance understanding of the edge of galaxy formation by showing how quickly star formation is halted in the faintest dwarf galaxies. Given the very low UFD stellar masses and large number of metallicity measurements, there is also a substantial chance to discover a surviving Population III star, which would be the first of its kind.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.