Explorations of the Milky Way's ``New'' Halo

银河系“新”光环的探索

• 批准号: 0307851
• 负责人: Steven Majewski
• 金额: $ 39万
• 依托单位: University of Virginia Main Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-08-15 至 2007-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0307851&HistoricalAwards=false
• 关键词: Explorations; Milky; Way; New; Halo

AST 0307851MajewskiCold dark matter (CDM) models for the growth of structure in the Universe predict the growth of large structures from the accumulation of smaller ones and the persistence of long-lived, "sub-halo" substructure within large halos. However, the number of observed satellites of the Milky Way is orders of magnitude less than predicted by most CDM models, and, if these sub-halos are dark, their presence should heat dynamically cold spiral disks, dwarf satellites and star clusters. Thus, considerable problems remain in refining the CDM paradigm to explain the evolution of galaxies like the Milky Way. If the Milky Way halo formed from the merger of luminous sub-halos, we expect to see substructure in the phase space distribution of halo stars, clusters and satellites. Due to Galactic tidal effects, this substructure would be in the form of streams of stars from the disrupted parent star systems, like those recently discovered coming from the Sagittarius (Sgr) dwarf spheroidal and the star cluster Palomar 5. Tantalizing evidence that the distribution of halo stars is very lumpy has been accumulating over the past decade. If the merged CDM sub-halos were dark, the coherence of star streams like Sgr and Pal 5 place strong constraints on the sub-halo mass spectrum.Dr. Steven Majewski and colleagues at the University of Virginia will acquire a more complete understanding of this "new" Milky Way halo by substantially expanding observational constraints on accreted substructure which set essential boundary conditions on current halo formation models. They will determine the actual filling factor of tidal debris and the likely mass spectrum of accreted entities. These measurements, in turn, permit inference of the Galactic mass distribution and the accretion history of the Galaxy. The program naturally expands upon previous work and approaches these questions from two directions: (1) The Galactic satellite system - objects that are most likely to be the prototypes of previously accreted entities, among which are current contributors to the accreted halo. First, this research team will undertake a comprehensive study of the Sgr dwarf spheroidal galaxy - the paradigm for Milky Way accretion - exploiting the clear, all-sky view of the Sgr core and tidal tails provided by the Two Micron All-Sky Survey. Second, they will continue the analysis of extended density profiles found around a number of Galactic dwarf spheroidal satellites, and ascertain whether these King profile "break populations" represent bound stellar halos or unbound tidal debris. Finally, they will expand the search for tidal disruption of Galactic satellites to the halo globular cluster system with a search for Pal 5 analogues. (2) The group will undertake a systematic search for substructure within the halo field star population using three large catalogues of K giant stars: the almost completed Grid Giant Star Survey, the companion Deep Giant Star Survey (DGSS), and a 225 square deg survey of K giants at the North Galactic Pole. In a pilot version of the DGSS, the team have undertaken observations in fields around the Magellanic Cloud periphery and uncovered substantial evidence for an outer halo that is highly networked by cold tidal streams and with no apparent contribution by a hot, pressure-supported component of halo stars. It is important to determine whether this finding is specific to regions near the Magellanic Clouds, or whether it represents the general character of the halo.A majority of the funds in this award are for direct support of undergraduate and graduate students who will participate substantially in the research efforts. Undergraduate involvement will include individual Senior Thesis research projects and assistance with the gathering of data as part of a semi-dedicated spectroscopic program at the local observatory. Dr. Majewski will continue his active public lecture commitment, and continue to work with the University of Virginia Digital Media Lab to produce animations and other graphics that enhance the explanation of Galactic structure science to the public.***

AST 0307851MAJEWSKICOLD暗物质（CDM）模型用于宇宙结构的生长，预测了大型结构的增长，从较小的结构的积累以及长寿命，“亚halo”子结构的持久性。然而，银河系的观察到的卫星数量比大多数CDM模型所预测的数量级要小，如果这些亚halos是黑暗的，则它们的存在应动态冷螺旋磁盘，矮卫星和恒星簇。因此，在完善CDM范式中仍然存在很大的问题，以解释银河系等星系的演变。如果银河系是由发光次荷拉斯的合并形成的，我们希望在光晕恒星，簇和卫星的相空间分布中看到子结构。由于银河系潮汐效应，该子结构将以破坏的母星系统的恒星流形式，就像最近发现的那些来自射手座（SGR）矮人球形球形和星团群palomar 5的形式。如果合并后的CDM次距离黑色是黑暗的，则在SGR和PAL 5之类的恒星流的相干性在下Halo质量频谱上放置了强限制。弗吉尼亚大学的史蒂文·马吉斯基（Steven Majewski）及其同事将通过大大扩展对当前光环形成模型的基本边界条件的观察性限制，从而对这种“新的”银河系光环有了更全面的了解。他们将确定潮汐碎片的实际填充因子和积聚实体的可能质谱。反过来，这些测量允许推断银河系分布和星系的积聚历史。该程序自然会扩展到以前的工作，并从两个方向上处理这些问题：（1）银河卫星系统 - 最有可能是先前积累实体的原型的对象，其中当前是积聚光环的当前贡献者。首先，该研究团队将对SGR矮人球形星系进行全面研究（银河系的范式增强范式） - 利用了两个Micron All -Sky调查提供的SGR核心和潮汐尾巴的清晰，全天的视图。其次，他们将继续分析围绕许多银河矮人球形卫星发现的扩展密度曲线，并确定这些王的概况“破裂种群”是否代表了结合的恒星光环还是未结合的潮汐碎片。最后，通过搜索PAL 5类似物，他们将扩大寻找银河卫星的潮汐破坏到Halo Globular群集系统。 （2）该小组将使用三个大型巨星的大型目录在Halo Field Star人群中进行系统的搜索：几乎完成的网格巨星测量，同伴Deep Giant Star Survey（DGSS）和225 Square deg的K巨人在North Galactic Pole上进行的K巨人。在DGSS的试点版中，该团队在麦哲伦云周围的田野上进行了观察，并发现了外部光环的大量证据，这是由冷潮汐流高度联网的，没有明显的贡献，没有光晕恒星的热压力，受压的成分。重要的是要确定这一发现是否针对麦哲伦云附近的地区，还是代表光环的一般特征。该奖项中的大部分资金是为了直接支持本科生和研究生，他们将大量参与研究工作。本科生的参与将包括个别高级论文研究项目，并在当地观测站的半专用光谱计划的一部分中收集数据。 Majewski博士将继续他的积极的公开演讲承诺，并继续与弗吉尼亚大学数字媒体实验室合作，制作动画和其他图形，以增强向公众的银河结构科学的解释。***