Interpretation of Galactic Chemical Evolution Surveys

温伯格博士和他的团队开发并应用了建模方法，以解释对数万或数十万颗恒星的大型光谱调查所测量的径向速度和多元素化学丰度。这样的研究对于提高我们对星系形成和星系化学演化的物理过程的理解是必要的。近期应用的主要重点是使用阿帕奇点天文台星系演化实验(APOEE)调查的数据，这是斯隆数字天空调查(SDSS-III)的后续调查。这项调查将测量银河系所有区域约10万颗红巨星的精确径向速度和多元素化学(约每颗恒星15种元素)。其他目标数据集包括斯隆银河系理解和探索扩展调查(SEGUE，SDSS的另一项后续调查)和太阳附近的径向速度实验(RAVE)调查，但也包括来自未来计划的其他大型调查的数据。这项研究使用了三种互补的建模方法：包括径向混合和动力学过程的解析化学演化模型，模拟孤立或存在卫星星系时星系盘增长的N体/流体动力学模拟，以及从完全宇宙初始条件模拟银盘形成。不断增长的圆盘模拟使用的是汽油代码，这也用于宇宙运行，但气体是作为半径和时间的规定函数添加到圆盘中的。这种方法提供了受控模拟，可以隔离特定物理过程的影响，并实现可用于区分诸如通过长期演化形成星系凸起和通过小型合并形成等过程的不同情景。研究人员将开发和应用主成分丰度分析(PCAA)技术来表征大型恒星数据集中元素丰度的任何相关变化。PCAA工具将是了解远地点化学丰度数据的系统效应和统计误差并以紧凑形式描述其多维测量的宝贵工具。这一工具和其他工具可能会增加SDSS-III数据集的影响。例如，通过将这些工具应用于远地点和其他数据集的解释，研究人员可以解决关于银河系厚盘、凸起和恒星晕的起源，以及薄盘内恒星的化学浓缩和迁移的历史的问题。PCAA和数据模型比较被用来分析恒星化学成分作为金属丰度和空间位置的函数的分布，并表征了银河系不同成分中化学动力学亚结构的水平。这可以限制卫星扰动和合并的重要性，通过从这些模式中确定主要的浓缩模式和罕见的离群值，人们可以洞察恒星核合成的关键路径。研究生和博士后研究人员参与了这个项目，并将接受开发和应用理论、观测和统计分析工具来解决星系形成和演化问题的培训。

Dr. Weinberg and his team develop and apply modeling methods to interpret measurements of radial velocities and multi-element chemical abundances from large spectroscopic surveys of tens or hundreds of thousands of stars. Such studies are necessary to improve our understanding of the physical processes in galaxy formation and galactic chemical evolution. The primary focus for near-term applications is to use data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey, which is a follow-up survey of the Sloan Digital Sky Survey (SDSS-III). This survey will measure precise radial velocities and multi-element chemistry (about 15 elements per star) for about 100,000 red giant stars in all regions of the Milky Way. Other target data sets include the Sloan Extension for Galactic Understanding and Exploration survey (SEGUE, another follow up survey to SDSS), and the Radial Velocity Experiment (RAVE) survey of the solar neighborhood, but also data from other large surveys planned in the future .The research employs three complementary modeling approaches: Analytic chemical evolution models that incorporate radial mixing and dynamical processes, N-body/hydrodynamic simulations that model growth of a galaxy disk either in isolation or in the presence of accreting satellite galaxies, and simulations of galactic disk formation from fully cosmological initial conditions. The growing disk simulations use the Gasoline code, which is also used in the cosmological runs, but gas is added to the disk as a prescribed function of radius and time. This approach provides controlled simulations that can isolate the effects of specific physical processes, and realize distinct scenarios that can be used to distinguish processes such as galactic bulge formation by secular evolution versus formation through minor mergers. The investigators will develop and apply the technique of Principal Component Abundance Analysis (PCAA) to characterize any correlated variations of elemental abundances in large stellar data sets. The PCAA tool will be a valuable tool for understanding systematic effects and statistical errors in the APOGEE chemical abundance data and for characterizing its multi-dimensional measurements in compact form. This and other tools are likely to increase the impact of the SDSS-III data sets. For example, by applying these tools to the interpretation of APOGEE and other data sets, the investigators can address questions about the origin of the Galactic thick disk, bulge, and stellar halo, and the history of chemical enrichment and migration of stars within the thin disk. The PCAA and data-model comparisons are used to analyze the distribution of stellar chemical compositions as a function of metallicity and spatial location, and to characterize the level of chemo-dynamical substructure in different components of the Galaxy. This can constrain the importance of satellite perturbations and mergers, and by identifying the principal patterns of enrichment and rare outliers from these patterns, one can gain insights insight into the key pathways of stellar nucleosynthesis. Graduate students and postdoctoral researchers are involved in this project and will be trained in developing and applying theory, observation, and statistical analysis tools to problems in Galaxy formation and evolution.