Mapping the Past in the Future: Science Enabled by High-Resolution Spectroscopic Stellar Surveys

约翰斯顿博士和她的团队通过详细的流体动力学和n体模拟，研究了矮星系的形成和演化，矮星系是我们当地宇宙中最常见的星系类型，以及银河系的形成。观测到的恒星的化学成分和它们今天的分布以及模拟被用来了解恒星晕中古老的吸积事件，并恢复对我们星系形成有贡献的祖先物体（例如矮星系和星团）的特性。这项研究的目的是通过将模拟结果与观测到的银河系所有组成部分的大样本中化学元素丰度的分布进行比较来重建银河系的过去，这些数据将从正在进行的和计划中的调查中获得（例如，阿帕奇角天文台银河演化实验（APOGEE）和英澳望远镜上的HERMES光谱仪）。在这里产生的银河系光晕的化学动力学形成模型也为解释来自恒星调查的大量数据集提供了指导。这些模型包括恒星形成、反馈和混合的物理学，并考虑到恒星形成的循环周期和垂死恒星喷出的新恒星形成区域的化学富集。预测的化学元素在不同恒星群中的丰度分布可以在恒星的光谱调查中探测到。半解析化学动力学模型的计划包括发展多区域描述的星系与无碰撞的恒星轨道允许恒星形成和化学元素的气体富集。为了更全面地了解星系晕的形成和演化，将星系的半解析化学动力学模型、完全自洽宇宙n体和流体动力学模拟结果结合起来；以及高维空间结构的统计分析。自洽模拟将用于改进在更简单的化学动力学模型中实现的内部重子物理和外部环境影响的描述。本研究计划为两名研究生提供研究课题。

Dr. Johnston and her team investigate the formation and evolution of dwarf galaxies, the most common type of galaxies in our local universe, and the formation of the Milky Way galaxy through detailed hydrodynamic and N-body simulations. The observed chemical composition of stars and their distribution today together with simulations is used to learn about ancient accretion events in the stellar halo, and to recover the properties of progenitor objects (e.g. dwarf galaxies and star clusters) that contributed to our galaxy's formation. The research aims to reconstruct the galaxy's past through comparing simulations to the observed distribution of the abundances of the chemical elements in large samples of stellar populations in all components of our Galaxy, which will become available from ongoing and planned surveys (e.g. with the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and the HERMES spectrometer on the Anglo-Australian telescope). The chemo-dynamical formation models of the Milky Way's halo that are produced here also provide guidance on the interpretation of large data sets from stellar surveys. The models include physics on star formation, feedback and mixing, and take into account the recurrent cycle of star formation and the chemical enrichment of new star-forming regions through ejecta from dying stars. The predicted abundance distributions of the chemical elements in different stellar populations might be detected in the spectroscopic surveys of stars. The plans for the semi-analytic chemo-dynamic models include the development of multi-zoned descriptions of the galaxy with collisionless stellar orbits allowing for star formation and enrichment of gas in chemical elements. In order to derive a more complete picture about the formation and evolution of the Galactic halo, results are combined from the semi-analytic chemo-dynamical models of galaxies, the fully self-consistent cosmological N-body and hydrodynamic simulations; and the statistical analyses of structures in high dimensional spaces. The self-consistent simulations will be used to refine the descriptions of internal baryonic physics and external environmental influences that are implemented in the simpler chemo-dynamical models. This research program provides research topics for two graduate students.