RUI: Reconstructing Galaxy Histories

了解星系的起源和演化是现代天体物理学的主要目标之一。人们普遍认为，星系是由原始物质分布中的微小密度波动形成的，随着时间的推移，重力会放大这种波动。然而，我们对星系形成过程的细节的了解仍然很不完整，许多重要的问题仍然没有答案。星系是如何形成的，又是什么时候形成的？它们是如何随着时间的推移而演变的？它们的周围环境如何影响星系的性质？在过去的几年里，迈克尔·韦斯特博士一直在进行一些原创的研究，无论是观察性的还是理论性的，以解决这些问题。有了这个奖项，他将在以往成功的基础上，探索可能导致对星系起源的进一步洞察的新途径。该项目的具体目标包括：o了解星系形成秘密的最有希望的方法之一是研究它们的球状星系团。球状星团是由多达100万颗恒星组成的密集聚集体，这些恒星通过相互引力被聚集在一起。大多数星系被数十个、数百个或数千个球状星团组成的系统所包围，这些星团就像蜂巢周围的蜜蜂一样蜂拥而至。今天的球状星系群体反映了数十亿年来通过合并和碰撞、吸积、几代恒星形成和其他过程正在进行的星系形成和演化的累积效应。因此，仔细分析星系的球状星团数量可以让天文学家重建其历史。韦斯特博士项目的一个主要目标是对处女座和彗星团中数百个星系的球状星系团进行迄今最全面的研究。O韦斯特博士和他的合作者最近发现了大量星际球状星团存在的证据，这些星系团并不受引力约束于单个星系，而是在星系团的核心自由漫游。这类新天体的发现是一个激动人心的结果，吸引了进一步的研究，目前正在附近的几个星系团中寻找星际球状恒星。这些银河系间球状星体的颜色、光度函数、空间和速度分布将对它们的起源产生强烈的制约。O越来越多的证据表明，星系毁灭可能比之前认为的要常见得多，星系的诞生和死亡是相互交织的。丰富的星系团是特别恶劣的环境，在这种环境下，小星系可能会被较大的星系蚕食，星系之间的碰撞会从它们的光晕中剥离物质，消融会去除它们的星际气体，星系在穿过星系团核心时可能会被潮汐场部分甚至完全撕裂。然而，一些星系的消亡也可能会产生新的星系，因为溢出到星际空间的物质最终会循环进入其他星系。这一研究项目的一个目标是进行第一次系统调查，以寻找星系团中被破坏的星系的微弱残骸，以便对目前密集环境中星系毁灭的速度施加定量限制。该奖项是在美国国家科学基金会本科生研究计划(RUI)的赞助下颁发的。***

AST 0205960WestUnderstanding the origin and evolution of galaxies is one of the major goals of modern astrophysics. It is generally believed that galaxies arose from small density fluctuations in the primordial matter distribution that were amplified over time by gravity. However, our knowledge of the details of the galaxy formation process is still far from complete, and many important questions remain unanswered. How and when did galaxies form? How have they evolved over time? How do their environs influence galaxy properties? Over the past few years, Dr. Michael West has been pursuing a number of original lines of research, both observational and theoretical, to address these questions. With this award he will build upon previous successes and explore new avenues that may lead to further insights about the genesis of galaxies. Specific goals of this project include the following: o One of the most promising ways to learn the secrets of galaxy formation is by studying their globular cluster populations. Globular clusters are dense aggregates of up to a million stars that are held together by their mutual gravitational attraction. Most galaxies are surrounded by systems of tens, hundreds, or thousands of globular clusters that swarm around them like bees around a hive. The present-day globular populations of galaxies reflect the cumulative effects of billions of years of ongoing galaxy formation and evolution via mergers and collisions, accretion, generations of star formation, and other processes. Careful analysis of a galaxy's globular cluster population can thus allow astronomers to reconstruct its history. A major goal of Dr. West's project is to undertake the most comprehensive study yet of the globular cluster systems of hundreds of galaxies in the Virgo and Coma clusters. o Dr. West and collaborators recently found evidence of the existence of a sizeable population of intergalactic globular clusters that are not gravitationally bound to individual galaxies but instead roam freely throughout the cores of galaxy clusters. The discovery of this new class of objects is an exciting result that invites further study, and searches for intergalactic globulars in several nearby galaxy clusters are currently underway. The colors, luminosity function, and spatial and velocity distributions of these intergalactic globulars will place strong constraints on their origin. o A growing body of evidence suggests that galaxy destruction might be a much more common occurrence than previously thought, and that the births and deaths of galaxies are intertwined. Rich galaxy clusters are especially harsh environments, where small galaxies can be cannibalized by larger ones, collisions between galaxies can strip material from their halos, ablation removes their interstellar gas, and galaxies may be partially or even completely torn apart by tidal fields as they travel through the cluster core. Yet the demise of some galaxies may also give rise to new ones, as material spilled into intergalactic space is eventually recycled into other galaxies. A goal of this research project is to conduct the first systematic survey to look for the faint remains of disrupted galaxies in galaxy clusters, in order to place quantitative constraints on the current rate of galaxy destruction in dense environments. This award is made under the auspices of the Research at Undergraduate Institutions (RUI) program at the NSF. ***