Extragalactic globular cluster systems as dynamical probes of galaxy formation and interaction

我们目前对星系的本质和起源的理解，很大程度上依赖于我们对丰富的、极其美丽的球状星团的仔细分析。球状星团包含已知的最古老的恒星，其中许多可以追溯到星系本身形成的时间。因此，它们是银河系早期历史的理想化石追踪器。一个典型的星团包含数十万颗相互引力拥抱的类似太阳的恒星，就像一群发光的蜜蜂。因此，每个球状星团都是超发光的，可以在遥远的星系中进行研究。(确实，许多目标星系距离数千万光年。)球状星团以数千万年或数亿年的时间递增地围绕其母星系旋转。使用地面或地球轨道上最大的反射望远镜，可以用光谱学来研究它们的轨道性质和化学成分。在早期宇宙中，恒星后来形成的原始气体几乎全部由最轻的元素组成：氢和氦。我们调查了光谱证据，证明自宇宙早期以来，球状星团内的恒星在组成上发生了多大的变化，并试图理解这与它们围绕母星系运动的动力学状态有何关系。近年来，相对年轻的球状星团的发现使人们对整个星系之间的相互作用和合并如何在星系的诞生和演化中发挥重要作用有了新的理解。例如，我们自己的银河系的命运，似乎不可避免地包括与附近的仙女座旋涡星系的合并--这一事件可能预示着10亿年后大量丰富星团的诞生。

Much of our current understanding of the nature and origin of galaxies depends on our careful analyses of the rich, supremely beautiful globular star clusters. The globular clusters contain the oldest known stars, and many of them date from the time of the formation of the galaxies themselves.  They are thus ideal 'fossil tracers' of a galaxy's  history.  A typical cluster contains hundreds of thousands of sun-like stars held in a mutual gravitational embrace, like a swarm of luminous bees.  Individual globular clusters are consequently ultra-luminous, and can be studied in remote galaxies.  (Indeed, many of the target galaxies are at distances of tens of millions of light years.)  Globular clusters orbit their parent galaxies on timescales of tens or hundreds of millions of years, and their orbital properties and chemical compositions can be studied spectroscopically, using the largest reflecting telescopes on the ground or in Earth orbit. In the early universe, the primordial gas out of which the stars would later form consisted almost entirely of the lightest elements: hydrogen and helium. We investigate the spectroscopic evidence for how much the stars within the globular clusters have changed in composition since the early stages of the universe, and seek to understand how that is related to their dynamical states of motions around the parent galaxies.    In recent years, discoveries of relatively young globular clusters have led to a fresh understanding of how interactions and mergers between entire galaxies can play an important role in galaxy birth and evolution.  The fate of our own Milky Way galaxy, for example, seems inevitably to include a merger with the nearby Andromeda spiral galaxy -- an event a billion years in the future which may be heralded by the spawning of large numbers of rich star clusters.