Collaborative Research: Star Formation Processes in Dwarf Galaxies

矮不规则星系是宇宙中最常见的星系类型。随着时间的推移，它们的演化相对缓慢，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，也没有切变。有些离我们很近，可以分辨出星团和恒星形成区域。因此，不规则矮行星是在原始环境中研究恒星形成的理想实验室。它们也有助于与螺旋进行比较，从而更好地理解两者。该项目的目标是确定是什么在大范围内调节矮星系中的恒星形成，然后将这些知识应用于其他星系。为什么普通矮星系的恒星形成率超过104倍，为什么年轻的恒星总是局限于星系内部区域，远离其他恒星和气体的径向范围？是什么决定了密集分子云的形成方式和位置？为了解决这些问题，洛厄尔天文台的黛德雷·亨特博士和IBM的布鲁斯·埃尔迈格林博士观察了139个相当正常、不相互作用、附近没有旋臂的星系。这些数据包括光学和近红外图像，这些图像可以确定这些星系一生中恒星的形成，原子HI图显示了原始云物质和云形成的环境，以及对产生恒星本身的温暖和寒冷分子云的观察。虽然先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品中HII区域的特性，包括它们的大小、压力、光度和位置。他们研究了LMC中的中性星际结构，并将所有数据结合起来，对NGC 2366进行了全面研究。这些结果导致了对恒星形成理论框架的修正：恒星形成的全局不稳定性和阈值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引力一样重要；湍流和相变通常将气体结构成云和云间介质，但整体扰动如条状和相互作用改变了这一点，产生异常的大质量束缚团。这些结果还通过说明壳层的膨胀和云的凝结如何在低切变下变得更加严重，增强了我们对正常螺旋星系中恒星形成过程的看法。有了这份新合同，研究人员将利用他们的大型、多波长调查来解决上述“大局”问题，从而完成项目。他们将发现矮星系中恒星形成是如何随时间和空间演变的；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反馈中的作用；并确定这些矮星的整体结构。这些结果中的许多将应用于其他星系类型和宇宙中的其他时代。＊＊＊

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. ***