Interpretation of Galactic Chemical Evolution Surveys

温伯格博士和他的团队开发并应用建模方法来解释从数万或数十万颗恒星的大型光谱调查中获得的径向速度和多元素化学丰度的测量结果。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。近期应用的主要焦点是使用来自阿帕奇点天文台银河演化实验（APOGEE）调查的数据，这是斯隆数字巡天（SDSS-III）的后续调查。这次调查将测量银河系所有区域大约10万颗红巨星的精确径向速度和多元素化学（每颗恒星大约15个元素）。其他目标数据集包括斯隆银河理解和探索扩展调查（SEGUE， SDSS的另一个后续调查），以及太阳附近的径向速度实验（RAVE）调查，以及计划在未来进行的其他大型调查的数据。该研究采用了三种互补的建模方法：包含径向混合和动力学过程的分析化学演化模型，在孤立或存在吸积卫星星系的情况下模拟星系盘生长的n体/流体动力学模拟，以及在完全宇宙学初始条件下模拟星系盘形成的模拟。不断增长的磁盘模拟使用了汽油代码，这也用于宇宙学运行，但气体作为半径和时间的规定函数添加到磁盘中。这种方法提供了可控的模拟，可以隔离特定物理过程的影响，并实现不同的场景，可用于区分过程，如星系隆起形成的长期演化与形成的小合并。研究人员将开发并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工具对于理解APOGEE化学丰度数据中的系统效应和统计误差以及以紧凑形式描述其多维测量将是一个有价值的工具。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APOGEE和其他数据集的解释，研究人员可以解决有关银河系厚盘、凸起和恒星晕的起源问题，以及薄盘内恒星化学富集和迁移的历史。利用PCAA和数据模型比较分析了恒星化学成分的分布作为金属丰度和空间位置的函数，并表征了银河系不同组成部分的化学动力学子结构水平。这可以限制卫星扰动和合并的重要性，并且通过识别富集的主要模式和这些模式中的罕见异常值，人们可以深入了解恒星核合成的关键途径。研究生和博士后研究人员将参与该项目，并将在开发和应用理论、观测和统计分析工具来解决星系形成和演化问题方面进行培训。

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.