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，矮星系是我们本地宇宙中最常见的星系类型，以及银河系的形成。今天观测到的恒星化学成分及其分布与模拟一起被用来了解恒星晕中古老的吸积事件，并恢复有助于我们星系形成的祖先物体（例如矮星系和星星团）的属性。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恒星群大样本中化学元素丰度分布进行比较，重建银河系的过去，这些数据将通过正在进行和计划进行的调查（例如，利用阿帕奇角天文台银河演化实验和英澳望远镜上的爱马仕分光计）获得。这里产生的银河系晕的化学动力学形成模型也为解释恒星巡天的大型数据集提供了指导。这些模型包括星星形成、反馈和混合的物理过程，并考虑了星星形成的循环和通过垂死恒星的喷出物在新的恒星形成区域中的化学富集。不同星族中化学元素丰度的预测分布可能在恒星的光谱巡天中被探测到。半解析化学动力学模型的计划包括发展多区描述的星系与碰撞恒星轨道允许星星的形成和丰富的气体化学元素。为了得到一个更完整的图片的形成和演化的银河系晕，结果相结合的半解析化学动力学模型的星系，完全自洽的宇宙学N体和流体动力学模拟，并在高维空间的结构的统计分析。自洽模拟将被用来完善内部重子物理和外部环境的影响，在更简单的化学动力学模型中实施的描述。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.