Galaxy Evolution Studies with Metal-deficient Blue Compact Dwarf Galaxies

缺乏金属的蓝致密矮星系的星系演化研究

• 批准号: 0205785
• 负责人: Trinh Thuan
• 金额: --
• 依托单位: University of Virginia Main Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-08-01 至 2008-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0205785&HistoricalAwards=false
• 关键词: Galaxy; Evolution; Studies; Metal; deficient

AST 0205785ThuanGalaxy formation is one of the most fundamental problems in astrophysics. Most high-z objectsobserved thus far are found to be rich in heavy elements, thus not qualifying as bona fide primevalgalaxies. An alternative approach is to search among nearby galaxies that may be actively formingstars for the first time at the present epoch. The best candidates for such a search are extremely metalpoor blue compact dwarfs (BCDs). They constitute excellent laboratories for pursuing the following cosmological problems. The standard hot big bang model of nucleosynthesis (SBBN) is one of the key quantitative tests of big bang cosmology. The primordial abundance Yp of 4He, together with that of Deuterium, is crucial for checking the consistency of SBBN. The relative insensitivity of 4He production to the baryonic matter density means that Yp needs to be determined to a precision of better than 1%. Dr. Trinh Thuan, at the University of Virginia, will evaluate systematic effects and correct Yp for them to attain that precision. He will search for more extremely metal-deficient BCDs in the newly released Sloan Digital Sky Survey spectral data base to improve the determination of Yp. The study of the BCD stellar populations will allow them to understand the properties of massive stellar populations in very low metallicity environments, like those prevailing in the era of galaxy formation. Moreover, Cold Dark Matter models predict that low-mass dwarf galaxies could still be forming at the present epoch because they originate from density fluctuations considerably smaller than those giving rise to the giant ones. Thus establishing the existence of young dwarf galaxies in the local universe will put strong constraints on the primordial density fluctuation spectrum. Dr. Thuan will apply age-dating techniques which he has developed and refined to a sample of very metal-deficient BCDs. There is a dichotomy in the way star formation proceeds in BCDs. In some, star formation occurs in a "passive" low-level diffuse fashion, with a low extinction. In others, "active" star formation occurs at a high level in Super Star Clusters, mixed with dense gas and a large amount of dust. Dr. Thuan will study the physical parameters whichgovern that dichotomy. Dr. Thuan will also study how the metallicity of the neutral gas compare with that of the ionized gas. Is the metallicity of the H ii region higher because of self-enrichment? Which constraints can be put on the time scale for the mixing of newly formed heavy elements in the H ii region with the HI gas? If the metallicity of the HI gas is very low, that would put constraints on the amount of metal pre-enrichment by the hypothetical Population III stars during the early pregalactic epoch. Such studies will shed new light on the study of abundances in high-redshift damped Lyman-alpha systems. Finally, Dr. Thuan will use these models to study correlations of the efficiency of mass exchange between the galaxy and its environment with global properties of BCDs such as their sizes, luminosities, metallicities, star formation rates, etc. ***

AST0205785团星系的形成是天体物理学中最基本的问题之一。到目前为止，大多数高z天体都被发现富含重元素，因此不符合真正的原始星系的条件。另一种方法是在附近的星系中搜索，这些星系可能是本时代第一次活跃地形成恒星。进行这种搜索的最佳候选者是极度贫金属化的蓝矮星(BCDS)。它们构成了研究下列宇宙学问题的极佳实验室。标准热大爆炸核合成模型(SBBN)是大爆炸宇宙学的关键定量检验之一。4He的原始丰度Yp和氘的原始丰度Yp对于检验SBBN的一致性是至关重要的。4He的产生对重子物质密度相对不敏感，这意味着需要将Yp的测量精度提高到1%以下。弗吉尼亚大学的Trin h Tuan博士将评估系统的影响，并为他们修正YP以达到那个精度。他将在最新发布的斯隆数字巡天光谱数据库中寻找更多极度缺乏金属的BCDS，以提高yP的测定。对BCD恒星群的研究将使他们能够了解在非常低的金属丰度环境中的大量恒星群的特性，就像在星系形成时代流行的那样。此外，冷暗物质模型预测，低质量矮星系在当前时代可能仍在形成，因为它们起源于密度波动，比产生巨型矮星系的密度波动小得多。因此，在局部宇宙中确定年轻矮小星系的存在将对原始密度涨落谱产生强烈的约束。Tuan博士将把他开发和改进的年龄测定技术应用到一个非常缺乏金属的BCDS样本中。在BCDS中，恒星形成的方式有两种。在某些情况下，恒星的形成是以一种“被动”的低层扩散方式进行的，消光程度很低。在另一些情况下，“活跃”恒星的形成发生在超星团的高水平上，混合着稠密的气体和大量的尘埃。特恩博士将研究支配这种二分法的物理参数。Tuan博士还将研究中性气体的金属含量与电离气体的金属含量的比较。HⅡ区的金属丰度高是因为自富集吗？对H II区新形成的重元素与HI气体混合的时间尺度可以施加哪些限制？如果HI气体的金属丰度非常低，这将限制假想的III族恒星在银河系早期的金属预富集量。这样的研究将为研究高红移阻尼莱曼-阿尔法系统的丰度提供新的线索。最后，特恩博士将使用这些模型来研究银河系及其环境之间的质量交换效率与BCDS的全球属性之间的相关性，这些属性包括它们的大小、亮度、金属度、恒星形成率等。