Are stellar halos the leftovers from galactic cannibalism?

这个项目旨在阐明星系的组装历史，特别是它们的恒星晕。在目前关于早期宇宙结构形成的概念图中，小的引力约束系统在数量上占主导地位，而现在的星系群是由这些原星系天体的多次合并形成的。宇宙学模拟预测，星系的扩展恒星成分是通过矮小星系的合并和潮汐分裂而建立的。由于这些区域的轨道时间很长，这种吸积的记忆应该以空间和/或速度的相干结构的形式持续存在。首席研究员和合作者已经确定并量化了银河系光晕中的这些结构。在这个项目中，他们将在6.5米的麦哲伦望远镜上进行一项观测计划，以绘制附近4个螺旋星系中微弱的、延伸的恒星晕，使绘制到这个深度的星系数量增加两倍。利用矮小星系吸积的N体模拟，他们将开发出晕结构的定量测量方法，这是吸积史的有效指标。然后，他们将把新的度量标准应用于他们对外部星系的新观测，以及斯隆数字天空调查和泛星1号调查中关于银河系光环的大规模调查数据。其目的是灵敏地测试恒星晕形成的理论。该项目将包括一名博士后研究员和本科生的专业培训和指导。首席调查员还将通过访问小学教室和协调努力改进在线参考维基百科的天文内容，参与外联活动。

This project aims to clarify the assembly histories of galaxies, focusing in particular on their stellar halos. In the current conceptual picture of structure formation in the early universe, small gravitationally bound systems dominate in number, and the present population of galaxies is formed by multiple mergers of these protogalactic objects. Cosmological simulations predict that the extended stellar components of galaxies are built up by the merging and tidal disruption of dwarf galaxies. Since orbital times are long in these regions, a memory of this accretion should persist in the form of coherent structures in space and/or velocity. The Principal Investigator and collaborators have identified and quantified these structures in the halo of the Milky Way. In this project they will carry out an observational program on the 6.5-meter Magellan telescope to map the faint, extended stellar halos in 4 nearby spiral galaxies, tripling the number of galaxies mapped to this depth. Using N-body simulations of dwarf galaxy accretion, they will develop quantitative measures of halo structure that are effective indicators of the accretion history. They will then apply the new metrics both to their new observations of external galaxies and to large-scale survey data on the halo of the Milky Way from the Sloan Digital Sky Survey and from the Pan-STARRS 1 survey. The goal is to sensitively test theories of stellar halo formation. The project will involve the professional training and mentoring of a postdoctoral researcher and undergraduate students. The Principal Investigator will also participate in outreach through visits to elementary school classrooms and a coordinated effort to improve the astronomical content of the on-line reference Wikipedia.