Collaborative Research: The Structure and Origin of the Galactic Halo

这是一个合作研究项目，涉及3个机构的科学家：亚利桑那大学的Edward Olszewski博士、密歇根大学的Mario Mateo博士和凯斯西储大学的Heather Morrison博士。这些研究人员正在绘制银河系中迄今为止无法到达的区域。他们将完成一项已经进行了几年的成像调查，他们将对调查中确定的候选晕星进行全面的光谱跟踪。这项调查是为了直接评估吸积在多大程度上形成了银河系的大部分光晕。这项调查的主要焦点是寻找居住在银河系晕外围的候选晕星。从这次调查中获得的最后一个光晕恒星样本将对光晕亚结构的存在进行严格的限制，如果它占光晕的10%到20%以上，就很可能提供这种结构的直接证据。天文学家对星系形成的看法正在发生深刻的变化，比如我们的星系。旧的观点认为外星系是在相对较短的时间内单一的、整体的坍缩，这一观点已经开始被这样的观点所取代，即银河系的大部分是在整个宇宙年龄内由更小的系统吸积而成的。大多数支持这种吸积驱动模型的数据都是间接的，并且涉及对星系如何在膨胀的宇宙中形成的复杂模型的期望。最近，人马座矮星系提供了强有力的证据，证明我们的光环恒星和星团至少有一部分来自一颗吸积的卫星。＊＊＊

AST 0098518OlszewskiThis is a collaborative research project involving scientists at 3 institutions: Dr. Edward Olszewski, at the University of Arizona, Dr. Mario Mateo, at the University of Michigan, and Dr. Heather Morrison, at Case Western Reserve University. These researchers are mapping a region of our Galaxy that was hitherto unreachable. They will complete an imaging survey that has been underway for several years, and they will carry out a comprehensive spectroscopic follow-up of halo-star candidates identified in the survey. The survey is undertaken to directly assess the degree to which accretion has formed the majority of the Galaxy's halo. The main focus of the survey is finding candidate halo stars that inhabit the outer parts of the Galactic halo. The final sample of halo stars from the survey will allow placement of strong limits on the existence of halo substructure and will very likely provide direct evidence of such structure if it comprises more than 10% to 20% of the luminous halo. A profound change is underway in how astronomers believe galaxies, such as ours, formed. Older notions of a single, monolithic collapse of the outer Galaxy on a relatively short timescale have begun to be superseded by the idea that much of the Galaxy formed from the accretion of much smaller systems over the entire age of the Universe. Most data supporting this accretion-driven model is somewhat indirect and involves expectations of sophisticated models of how galaxies form in an expanding Universe. Recently, the Sagittarius dwarf galaxy has provided strong evidence that at least part of our halo stars and clusters have come from an accreted satellite. ***