Metallicity Distributions of the Faintest Dwarf Galaxies

最暗矮星系的金属丰度分布

• 批准号: 2307599
• 负责人: Alexander Ji
• 金额: $ 45.92万
• 依托单位: University of Chicago
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-09-01 至 2026-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2307599&HistoricalAwards=false
• 关键词: Metallicity; Distributions; Faintest; Dwarf; Galaxies

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.

超微弱矮星系（UFD）似乎是已知最古老、暗物质最多、金属最贫乏的星系。它们的所有恒星似乎都是在宇宙存在的最初 1-20 亿年期间形成的。因此，它们的恒星族保留了有关这个早期时期工作过程的重要信息，包括第一代恒星（族III）的形成和再电离。虽然高红移 UFD 太微弱，连 JWST 都无法研究，但原则上附近的例子应该能够产生足够的信息来重建其形成历史并限制星系的形成。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量来推导出附近四个 UFD 中每一个的 50-200 个主序关闭 (MSTO) 恒星的金属丰度，这比测得的化学丰度的数量增加了一倍多。对由此产生的金属丰度分布函数（MDF）的分析有望得出这些天体的精确恒星形成历史，从而为第一个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能够在观测到的 MSTO 恒星中检测到单独的 III 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以及代表性不足的本科生的研究经验。 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对每个目标 UFD 星系中 50-200 颗 MSTO 恒星进行金属丰度测量的深度光谱。这将为这些系统的化学演化建模提供迄今为止最大的金属丰度样本。该团队将打破基于等时线的恒星形成历史中的年龄金属性简并，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当量宽度来确定。这些将产生最佳测量的 UFD 形成历史，这将使这些数据作为化学演化或流体动力学星系形成模拟的测试变得非常有价值。这些形成历史将通过显示最微弱的矮星系中恒星形成停止的速度来促进对星系形成边缘的理解。鉴于 UFD 恒星质量非常低和大量金属丰度测量，还有很大机会发现幸存的星族 III 恒星，这将是同类中的第一颗。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。