Atomic Hydrogen As A Probe Of Molecular Cloud Structure And Evolution

原子氢作为分子云结构和演化的探针

• 批准号: 0404770
• 负责人: Paul Goldsmith
• 金额: --
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-07-01 至 2008-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0404770&HistoricalAwards=false
• 关键词: Atomic; Hydrogen; Probe; Molecular; Cloud

Dr. Paul Goldsmith will use this award to pursue a novel probe of molecular cloud structure for the study of HI narrow line self absorption, or HINSA. While there have been many advances in our understanding of the dense, cold regions where new stars form, there remain many important questions. These include (1) the structure of molecular clouds including heating and cooling processes which determine their temperature and ionization state; (2) the lifetime of molecular clouds, in particular related to the time scale for star formation; and (3) the role of the magnetic field. The observations of the 21cm line will yield vital information, complementary to that obtained from higher frequency observations of molecules and dust. This research project will enhance our understanding of molecular clouds and how new stars are formed by providing important information on key processes in dense regions, including the grain surface H2 formation and the cosmic ray heating rate, by giving important information on the lifetime of molecular clouds; in particular the time delay between the onset of atomic to molecular conversion and the formation of new stars, by developing a new technique for measuring the magnetic field in dense regions, with much enhanced sensitivity, and by offering the capability of producing maps of line of sight magnetic field strength in a reasonable time.Molecular hydrogen is the most abundant molecule in dense, well shielded regions of the interstellar medium, but is extremely difficult to trace directly. It now appears possible, that by careful measurements of the atomic hydrogen associated with dense molecular cloud cores, we can learn much about the transition from atomic to molecular form and thus of the evolution of dense regions, starting from being nearly atomic and ending up as largely molecular. The HI/H2 ratio can serve as a chronometer for the evolution of interstellar clouds and measure their evolution towards the phase in which they are the sites of star formation. The magnetic field and its interaction with matter are critical for a number of processes that occur in the interstellar medium, including star and planet formation. This importance has motivated many researchers,but there is very little information about the initial conditions in terms of magnetic field strength, for core evolution and collapse. It is plausible that the present work will prove so effective a method of Zeeman determination of the magnetic field, that there will for the first time be maps of the magnitude of the (line of sight) value of the magnetic field in dense clouds. These data will be a strong motivation for continued theoretical studies on a range of magnetohydrodynamic (MHD) topics, including studies of MHD turbulence and its decay in dense clouds and the relationship of the magnetic field to disks, jets, and molecular outflows. The new results will address questions closely tied to many important issues in astronomy including the initial mass function and the chemical evolution of galaxies. The topic of star formation is clearly of wide interest Groups of senior citizens, university retirees, and students at purely undergraduate institutions all see molecular clouds and star formation as topics to which they can relate. It is anticipated that in the course of this research program, Dr. Goldsmith. will continue to give talks to these groups. By connecting the issue of the chemistry in molecular clouds to that in the primitive solar system, and by linking the magnetic field we are studying to that in protostellar disks such as that from which our solar system formed, this work will have an impact on a broad audience. ***

Paul Goldsmith博士将利用这一奖项来探索分子云结构的新探测器，以研究HI窄线自吸收或HINSA。虽然我们对形成新恒星的密集、寒冷区域的理解已经取得了许多进展，但仍然有许多重要的问题。这些包括(1)分子云的结构，包括加热和冷却过程，这决定了它们的温度和电离状态；(2)分子云的寿命，特别是与恒星形成的时间尺度有关；以及(3)磁场的作用。对21厘米谱线的观测将产生重要信息，补充从分子和尘埃的高频观测中获得的信息。这个研究项目将通过提供关于密集区域关键过程的重要信息，包括颗粒表面H2的形成和宇宙线加热率，通过提供关于分子云寿命的重要信息，来加强我们对分子云和新星形成的理解；特别是从原子到分子的转变开始到新星形成之间的时间延迟，通过开发一种新的技术来测量密集区域的磁场，大大提高了灵敏度，并提供了在合理时间内绘制视线磁场强度图的能力。分子氢是星际介质密集、屏蔽良好的区域中最丰富的分子，但极难直接追踪。现在看来，通过仔细测量与致密分子云核相关的原子氢，我们可以了解许多从原子形式到分子形式的转变，从而了解致密区域的演化，从接近原子开始，最终以分子为主。HI/H2比率可以作为星际云演化的计时器，并测量它们向恒星形成地点所处阶段的演化。磁场及其与物质的相互作用对星际介质中发生的许多过程至关重要，包括恒星和行星的形成。这一重要性激励了许多研究人员，但关于磁场强度的初始条件，即核心演化和崩塌的信息很少。有可能的是，本工作将证明塞曼测定磁场的方法是如此有效，以至于将第一次有稠密云中磁场(视线)值的量值的地图。这些数据将是对一系列磁流体动力学(MHD)主题继续进行理论研究的强大动力，包括研究MHD湍流及其在稠密云中的衰减，以及磁场与圆盘、喷流和分子外流的关系。新的结果将解决与天文学中许多重要问题密切相关的问题，包括初始质量函数和星系的化学演化。恒星形成的话题显然引起了广泛的兴趣，老年人、大学退休人员和纯本科院校的学生都认为分子云和恒星形成是他们可以联系到的话题。预计在这个研究项目的过程中，戈德史密斯博士。将继续向这些团体发表演讲。通过将分子云中的化学问题与原始太阳系中的化学问题联系起来，并将我们正在研究的磁场与太阳系形成的原恒星盘中的磁场联系起来，这项工作将对更广泛的受众产生影响。***