A Systematic Search for Stars in Almost-Dark Galaxies

星系是恒星、气体、尘埃和暗物质的集合体，它们都通过引力聚集在一起。自从美国天文学家埃德温·哈勃首次证明星系是由数十亿颗恒星组成的孤岛宇宙以来，已经过去了近100年。研究人员试图了解星系是如何形成和随时间变化的。他们的目标是确定产生了所观察到的各种星系的恒星形成过程。研究人员选择了一组附近富含气体的星系进行特别研究。这些星系是用阿雷西博射电望远镜发现的。这些星系含有大量的中性氢(HI)气体，这是新一代恒星的原始成分。此外，参与该项目的研究生和本科生将接受科学研究、技术和数学方法、图像处理和分析以及计算机编程方面的专业发展和培训。紫花苜蓿调查是一项HI调查，旨在建立一个统计上完整的本地宇宙中性氢气普查。紫花苜蓿覆盖了7000平方度的天空，已经编目了3万个物体。该项目旨在测量两种特定类型的紫花苜蓿源的光学性质：超致密高速云团(UCHVCs)，它是中性氢气云，其性质使其成为附近低质量星系的理想候选者；以及“几乎暗”星系，它是具有更大可能距离和质量范围的HI源。这两类天体在现有的星表中都没有明确的光学对应关系，因此我们的目标是探测和表征这些天体的光发射，以便更好地了解它们的性质和演化状态。为了实现这一目标，研究人员和她的学生将使用WIYN 3.5米望远镜和1度成像仪(ODI)获取和分析深部、广域、光学成像，这些成像样本是从紫花苜蓿中挑选的UCHVC和几乎黑暗的星系的清晰样本。这些观测将被用来研究UCHVC和几乎黑暗样本的性质，并解决关于中性气体星系如何形成和演化的重要问题。这些问题包括：UCHVC对“卫星失踪问题”有什么影响？有多少UCHVCs拥有可检测到的恒星种群？星系的环境和在局部体积内的位置与它们的性质(例如，是否存在正在形成的恒星、它们的演化阶段)之间是否存在关联？近暗星系的性质是什么，它们的性质在光学星表上与“正常”星系有何不同？这些近暗的天体揭示了恒星是如何在处于HI质量到光学光度的极端末端的星系中形成的？UCHVCS样本中的天体还可以用来描述低质量星系(小于1000万个太阳质量)的重子Tully-Fisher关系，并探索宇宙的化学演化。研究人员对研究生和本科生的支持和指导，以及对学生研究能力的培训做出了重大承诺。这位研究人员还将与印第安纳大学创新教学中心的顾问合作，修改一门面向非专业学生的大型天文学入门课程。研究人员将在一门课程中使用光学和射电望远镜获取的数据来激发学生的兴趣，帮助说明正在教授的概念，并展示现代天文学研究如何进行的具体例子。最后，这位研究人员将通过她在玛丽亚·米切尔协会董事会的成员身份，致力于推动科学推广和教育。玛丽亚·米切尔协会是一个非营利性的研究、教育和推广组织，旨在促进美国第一位女性职业天文学家的遗产。

Galaxies are collections of stars, gas, dust, and dark matter, all held together by gravity. It is nearly 100 years since American Astronomer Edwin Hubble first showed that galaxies are island universes, containing of billions of stars. The investigators seek to understand how galaxies form and change over time. Their goal is identifying the star formation processes that produced the wide variety of galaxies observed. The investigators have selected for special study a set of nearby, gas-rich, galaxies. These galaxies were found with the Arecibo radio telescope. These galaxies contain large amounts of neutral hydrogen (HI) gas, the raw ingredient of new generations of stars. Furthermore, graduate and undergraduate students who work on the project will receive professional development and training in scientific research, technical and mathematical methods, image processing and analysis, and computer programming.The ALFALFA survey is a HI survey aimed at constructing a statistically-complete census of neutral hydrogen gas in the local universe. ALFALFA covers 7000 square degrees of sky and has cataloged 30,000 objects. This project aims to measure the optical properties of two specific types of ALFALFA sources: Ultra-Compact High Velocity Clouds (UCHVCs), which are neutral hydrogen gas clouds with properties that make them good candidates for nearby low-mass galaxies, and "Almost-Dark" galaxies, which are HI sources with a wider range of possible distances and masses. Both classes of objects have no clear optical counterpart in existing catalogs, so the objective is to detect and characterize the optical emission from these objects in order to better understand their properties and evolutionary state. To accomplish this objective, the investigator and her students will obtain and analyze deep, wide-field, optical imaging with the WIYN 3.5-meter telescope and One Degree Imager (ODI) of a well-defined sample of UCHVCs and Almost-Dark galaxies chosen from ALFALFA. The observations will be used to investigate the properties of the UCHVC and Almost-Dark samples and address important questions about how galaxies with neutral gas form and evolve. These questions include: What implications do the UCHVCs have for the ``missing satellites problem''? What fraction of the UCHVCs have detectable stellar populations? Are there correlations between the galaxies' environments and locations within the Local Volume and their properties (e.g., the presence or absence of ongoing star formation, their evolutionary phase)? What is the nature of the Almost-Dark galaxies, and how do their properties differ from ``normal'' galaxies in optical catalogs? What do the Almost-Dark objects reveal about how star formation takes place in galaxies at the extreme end of the HI mass to optical luminosity regime? The objects in the UCHVCs sample can also be used to help characterize the Baryonic Tully-Fisher Relation down to very low galaxy masses (less than ten million solar masses) and to probe the chemical evolution of the Universe.The investigator has made major commitments to the support and mentoring of graduate and undergraduate students, and to the training of students in research. The investigator will also work with consultants at the Indiana University Center for Innovative Teaching and Learning to revise a large introductory astronomy course for non-majors. The investigator will use the data taken with optical and radio telescopes in a course to pique student's interest, help illustrate the concepts being taught, and show concrete examples of how modern research is done in astronomy. Finally, the investigator will work on advancing science outreach and education through her membership on the Board of Directors of the Maria Mitchell Association, a non-profit research, education, and outreach organization that promotes the legacy of America's first female professional astronomer.