Direct Modeling of Star Clusters in Galaxy Formation Simulations

科学家们将对我们银河系恒星群的起源进行数值模拟。这项研究将包括一种在星系形成模拟中直接对星团进行建模的新方法。他们试图解开我们对银河系形成和演化理解中的几个悬而未决的谜团：(I)是什么原因导致大质量球状星团中的多代恒星？(Ii)从球状星团中剥离的晕星的比例是多少？(Iii)这个凸起是由早期的合并形成的，还是由银河盘的逐渐转变形成的？他们将在宇宙学自适应网格精化代码(ART)中实现星系团形成和演化模型，并运行具有不同环境和合并历史的几个银河系大小的星系的实现。ART是一个强大的星系形成代码，它已经包括宇宙气体的非平衡冷却和加热，分子氢的非平衡形成和解离，年轻恒星的热、动力学和辐射反馈，电离辐射的传输，以及其他重要过程。星团恒星的形成将增加对恒星群体的真实描述，具有定义明确的恒星初始质量函数和对星际介质(ISM)更集中的反馈。这些模拟将产生一个丰富的数据模型，并将用于解释对星系团和矮星的各种观测。它们将把模拟整合到一个关于宇宙时间内星系形成的最先进的科学可视化程序中。这些可视化图像将在密歇根大学天文馆展出，底特律大都市区的数千名小学生、初中生和高中生将可以观看。

The scientists will numerically simulate the origin of star populations in our Galaxy. The study will include a novel approach to modeling star clusters directly in galaxy formation simulations. They seek to unravel several unsolved puzzles in our understanding of Galactic formation and evolution: (i) What caused multiple generations of stars within massive globular clusters? (ii) What is the fraction of halo stars stripped off globular clusters? (iii) Was the bulge assembled by early mergers or by gradual transformation of the Galactic disk? They will implement the cluster formation and evolution model in the cosmological adaptive-mesh-refinement code (called ART) and run several realizations of Milky Way-sized galaxies with different environment and merger history. ART is a powerful galaxy formation code and already includes non-equilibrium cooling and heating of cosmic gas, non-equilibrium formation and dissociation of molecular hydrogen, thermal, kinetic, and radiative feedback of young stars, transport of ionizing radiation, and other important processes. Inclusion of clustered star formation will add a realistic description of stellar populations, with a well-defined stellar initial mass function and more concentrated feedback on the interstellar medium (ISM). The simulations will produce a rich data model, and will be used to interpret various observations of Galactic clusters and dwarf satellites.They will integrate the simulations into a program of state-of-the-art scientific visualizations of galaxy formation over cosmic time. The visualizations will be designed for display at the University of Michigan Planetarium, and will be viewed by thousands of elementary, middle and high school students in the Detroit metropolitan area.