Collaborative Research: Star Formation Processes in Dwarf Galaxies

AST 0204922猎人矮星不规则星是宇宙中最常见的星系类型。随着时间的推移，它们的演化速度相对较慢，在化学上类似于今天的螺旋星系和高红移的年轻星系的外部。它们没有密度波，切变很小。其中一些距离我们非常近，可以分辨出星团和恒星形成区域。因此，矮星不规则星是研究原始环境中恒星形成的理想实验室。这个项目的目标是确定是什么在大范围的尺度上控制着矮小星系的恒星形成，然后将这一知识应用于其他星系。为什么正常矮星系的恒星形成率超过104倍，为什么年轻恒星总是局限在星系内部，远离其他恒星和气体的径向范围？是什么决定了致密分子云的形成方式和位置？为了解决这些问题，洛厄尔天文台的迪德雷·亨特博士和IBM的布鲁斯·埃尔梅格林博士观察到了139个没有旋臂的附近星系，这些星系相当正常，没有相互作用。这些数据包括光学和近红外图像，可以在这些星系的生命周期内确定恒星的形成，原子HI图显示了云形成的原始云物质和环境，以及对孕育恒星本身的温暖和寒冷分子云的观测。尽管之前的资助强调数据收集和处理，但这些研究人员已经分析了样本中HII区域的属性，包括它们的大小、压力、亮度和位置。他们研究了LMC中中性的星际结构，并结合所有数据对NGC 2366进行了全面研究。这些结果导致了恒星形成理论框架的修订：全球不稳定性和恒星形成的门槛柱密度不如局部过程和条件重要；星际介质的热平衡性质与自重一样重要；湍流和相变通常将气体结构化为云和云间介质，但全球扰动(如棒和相互作用)会改变这一点，产生异常质量的束缚星团。这些结果也增强了我们对正常螺旋星系恒星形成过程的看法，因为它说明了壳层的膨胀和云的凝聚在低切变时变得更加严重。有了这个新的奖项，研究人员将利用他们的大型多波长调查，通过解决上面提出的“大画面”问题来完成该项目。他们将发现矮小星系中恒星形成是如何在空间和时间上演变的；考虑星系边缘的特殊效应；展示恒星形成历史与气体结构和其他云形成条件的关系；确定不同大小和密度的恒星形成区域的形成要求；确定星际介质的孔隙度及其在可能的反馈中的作用；以及确定矮星的整体结构。其中许多结果将适用于其他星系类型和宇宙中的其他纪元。***

AST 0204922HunterDwarf irregulars are the most common type of galaxy in the Universe. They evolve relatively slowly over time and chemically resemble the outer parts of present-day spirals and young galaxies seen at high redshift. They have no density waves and little shear. Some are very close to us, permitting the resolution of clusters and star-forming regions. As a result, dwarf irregulars are ideal laboratories for studies of star formation in a pristine environment. They are also useful for comparisons with spirals, leading to a better understanding of both.The goals of this project are to determine what regulates star formation in dwarf galaxies on a wide range of scales, and then to apply this knowledge to other galaxies. Why do star formation rates in normal dwarf galaxies span a factor of over 104, and why are young stars always limited to the inner galaxy regions, far inside the radial extent of other stars and gas? What governs how and where dense molecular clouds form? To address these questions, Dr. Deidre Hunter, at Lowell Observatory, and Dr. Bruce Elmegreen, at IBM, have observed 139 reasonably normal, non-interacting, nearby galaxies without spiral arms. The data include optical and near-infrared imagesthat allow the star formation to be determined over the lifetimes of these galaxies, atomic HI maps that show the raw cloud material and environment for cloud formation, and observations of the warm and cold molecular clouds that give birth to the stars themselves. Although a previous grant emphasized data collection and processing, these investigators have already analyzed the properties of the HII regions in the sample, including their sizes, pressures, luminosities, and locations. They studied the neutral interstellar structure in the LMC and combined all their data for a comprehensive study of NGC 2366. The results have led to a revision in the theoretical framework for star formation: global instabilities and threshold column densities for star formation are less important than local processes and conditions; the thermal equilibrium properties of the interstellar medium are as important as self-gravity; turbulence and phase changes generally structure the gas into cloud and intercloud media, yet global disturbances such as bars and interactions change this, producing anomalously massive bound clusters. The results have also enhanced our perspective on star formation processes in normal spiral galaxies by illustrating how the expansion of shells and the condensation of clouds becomes more severe at low shear. With this new award, the investigators will capitalize on their large, multi-wavelength survey to finish the project by addressing the "big-picture" questions posed above. They will find how star formation evolves over space and time in a dwarf galaxy; consider the special effects at galaxy edges; show how the star formation history relates to the gas structure and other conditions for cloud formation; determine the formation requirements for star forming regions of different sizes and densities; determine the porosity of the interstellar medium and its role in possible feedback; and determine the overall structure of the dwarfs. Many of these results will have applications to other galaxy types and to other epochs in the Universe. ***