Formation and Evolution of the Milky Way

星系中古老的、贫金属的恒星晕的结构、运动学和化学性质长期以来为星系的早期形成历史提供了有价值的信息，特别是在局部群中的星系。例如，观测到的银晕恒星的化学性质和动力学性质之间的关联，或者没有这种关联，使作者能够讨论银河系是否是在几个动力学时间尺度内由整体坍塌形成的。基于冷暗物质模型的星系形成的数值模拟表明，盘状星系中贫金属的古老恒星晕形成的基本物理过程是由星系下团块在高红移时引力收缩过程中的耗散和无耗散合并及其所产生的潮汐扰动来描述的：因此，对星系下团团(即低质量矮星的前身)恒星形成和化学演化史的理解是…的此外，尽管年轻宇宙中的许多观测和理论研究已经为宇宙再电离历史提供了重要的限制，但以下问题在当今宇宙中仍有待探索：(1)旧星系的恒星晕是否包含再电离历史的化石记录；(2)对恒星晕的观测可以提供什么线索，以了解再电离对星系形成过程的可能影响。最近，哈勃太空望远镜和大型地面望远镜研究了超出局部群的星系中贫金属的旧恒星晕的物理性质。此外，最近的数值研究对再电离影响下的矮小星系的恒星形成历史提供了一些具体的预测。因此，基于观测结果和数值模拟结果的比较来讨论上述问题是非常及时的。利用这次获奖的机会，我们在银河系和本星系群星系的形成和演化的其他相关问题上取得了许多进展。此外，我们还研究了星系可见部分周围暗物质的结构，这被认为在星系的形成过程中通过等级聚类发挥了重要作用。为此，我们重点研究了背景源(如类星体)上的引力透镜现象，以限制透镜星系中的质量亚结构。对这一问题进行了观测和理论分析。较少

Structural, kinematical, and chemical properties of old, metal-poor stellar haloes of galaxies have long provided valuable information on early formation histories of galaxies, in particular; galaxies in the Local Group. For example, the observed correlation between chemical and dynamical properties of Galactic halo stars or lack thereof have enabled authors to discuss whether the Galaxy was formed by a monolithic collapse within a few dynamical timescales. Numerical simulations of Galaxy formation based on the cold dark matter model have demonstrated that basic physical processes involved in the formation of the metal-poor, old stellar halo in a disk galaxy are described by both dissipative and dissipationless merging of subgalactic clumps and their resultant tidal disruption in the course of gravitational contraction of the galaxy at high redshift : Thus, understanding of star formation and chemical evolution histories in subgalactic clumps (i.e., progenitors of low-mass dwarfs) are … More key for better understanding of the origin of galactic stellar halos.Also, although many observational and theoretical studies in the young universe have already provided important constraints on the cosmic reionization history, it remains yet to be explored in the present-day universe as to (1)whether old stellar halos of galaxies contain the fossil records of reionization history and (2)what observations of stellar halos can provide what clues to the possible influences of reionization on galaxy formation processes. Physical properties of metal-poor, old stellar halos in galaxies beyond the Local Group have been recently investigated by the Hubble Space Telescope and large ground--based telescopes. Furthermore, recent numerical studies provided some specific predictions on star formation histories of dwarf galaxies under the influence of reionization. Thus it is quite timely to discuss the above questions based on the comparison between observations and numerical simulations addressing the possible influence of reionization on the properties of galactic stellar halos.Taking advantage of this grant awarded, we have made a lot of progresses about the above issue as well as other relevant issues on the formation and evolution of the Milky Way and Local Group galaxies. Furthermore, we have studied the structure of dark matter surrounding the visible parts of galaxies, which is supposed to play an important role in the formation process of galaxies through hierarchical clustering. For this purpose, we have focused on gravitational lensing phenomena on background sources (such as QSOs), to set limits on mass substructure in lensing galaxies. Both observational and theoretical analyses have been made on this issue. Less