The Role of Magnetic Fields in Star Formation: Polarization Observations of Molecular Clouds

磁场在恒星形成中的作用：分子云的偏振观测

• 批准号: 1007713
• 负责人: Richard Crutcher
• 金额: $ 24.57万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-08-15 至 2014-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1007713&HistoricalAwards=false
• 关键词: Role; Magnetic; Fields; Star; Formation

Understanding star formation is one of the outstanding problems in modern astrophysics and whether magnetic fields play a role in regulating the star formation process is a major question. What is the relative importance of magnetic fields and turbulence in the formation of gravitationally bound interstellar clouds and cores and their subsequent collapse to form stars? Only observations of magnetic fields in dense molecular clouds can test the theoretical predictions of magnetically dominated star formation and validate or eliminate this model. This proposal is the continuation of the long-term and successful research program of Professor Richard Crutcher to observe magnetic fields in molecular clouds with the specific focus of testing star formation theory. These observations will be done over the three-year grant period. First, observations of the Zeeman splitting in spectra of the molecules CN and C2H at 3-mm wavelength will be done with the 30-m telescope of the ?Institut de Radio Astronomie Millimétrique? (IRAM) in Spain. This will give measurements of the line-of-sight magnetic field strengths toward a significant sample of dense molecular cloud cores. Second, synthesis imaging of CN and C2H Zeeman targets selected from the IRAM sample with the Atacama Large Millimeter Array (ALMA) is planned, together with ALMA synthesis imaging of linearly polarized dust emission and linearly polarized spectral line emission from multiple molecular species.Many of the ALMA observations can be done simultaneously. By the end of the proposed grant period, a significant number of single-dish Zeeman observations will be at hand that a Bayesian statistical analysis can be carried out to infer the probability distribution function of the total magnetic field strength from the measured line-of-sight strengths. The work from this proposal will give sensitive ALMA maps of high-density molecular regions for the line-of-sight component of the magnetic field in two molecular species that sample different density regimes. In addition it will give plane-of-sky maps from dust emission that samples the entire line of sight and from linearly polarized spectral lines in multiple molecular transitions that sample different layers of clouds as well as bipolar outflows. In addition a computer code will be created that generates maps from 3D models or simulations of molecular cloud density and magnetic field structures exactly as they would be observed with ALMA. Then a comparison of ALMA maps with model maps can be used to infer the 3D structure of magnetic fields and to test the predictions of star formation theories. By the end of the grant period, the researchers expect a significant advance in understanding the role of magnetic fields in star formation.Broader Impacts: The research proposed here has broader impacts in multiple areas of star formation studies. Examples of such impact are: An improved recipe for star formation for use in large-scale structure formation and galaxy evolution simulations; improved mass estimates of molecular clouds based on the virial theorem (where magnetic pressure is generally ignored); and improved understanding of the role of magnetic fields in the generation of bipolar winds from young stars and even Active Galactic Nuclei (AGNs). This project will also help to enhance the infrastructure for research and education, in particular, the ALMA facility and instrumentation. Polarimetry with a synthesis-imaging array has many potential pitfalls, and ALMA has the goal of reaching its full capability for polarization mapping. This group will be among the first users of ALMA and will bring its expertise and experience in interferometric polarimetry to bear such that ALMA will be able to do polarization science optimally as early as possible. This will include involvement with ALMA hardware commissioning and testing the ALMA software for polarization imaging and providing modeling code to the scientific community, so that the results of ALMA polarization mapping may be fully exploited by all users. In addition, a graduate student will be trained in the observational and analytical techniques. With ALMA coming on line in the near future, it is critical that students are trained in areas relevant to ALMA research. The principal investigator has a history of training students in radio polarimetry, and will continue to train PhD students who will be able to make full use of ALMA.

理解星星的形成是现代天体物理学中的一个突出问题，磁场是否在星星的形成过程中起着调节作用是一个重大的问题。磁场和湍流在引力束缚的星际云和核心的形成以及它们随后的坍缩形成恒星的过程中的相对重要性是什么？只有在致密分子云中观测磁场，才能检验磁主导星星形成的理论预测，并验证或消除这个模型。这一建议是Richard Crutcher教授长期成功研究计划的延续，该计划旨在观察分子云中的磁场，并特别侧重于测试星星形成理论。这些观察将在三年赠款期内进行。首先，塞曼分裂的分子CN和C2 H在3毫米波长的光谱观测将与30米望远镜的？射电天文学研究所？（IRAM）在西班牙。这将提供对致密分子云核心的重要样本的视线磁场强度的测量。其次，利用阿塔卡马大毫米波阵（阿尔马）对IRAM样品中CN和C2 H塞曼靶进行合成成像，并对线偏振尘埃辐射和多分子线偏振谱线辐射进行阿尔马合成成像，其中多个阿尔马观测可以同时进行。在拟议的资助期结束时，将有大量的单碟塞曼观测数据，可以进行贝叶斯统计分析，从测量的视线强度推断总磁场强度的概率分布函数。从这个建议的工作将给出灵敏的阿尔马地图的高密度分子区域的视线组成部分的磁场在两个分子物种，样品不同的密度制度。此外，它还将提供来自尘埃排放的天空平面图，对整个视线进行采样，并从多个分子跃迁中的线性偏振光谱线中采样不同的云层以及双极外流。此外，将创建一个计算机代码，从分子云密度和磁场结构的3D模型或模拟生成地图，就像用阿尔马观察到的那样。然后，将阿尔马图与模型图进行比较，可以用来推断磁场的三维结构，并检验星星形成理论的预测。到资助期结束时，研究人员预计在理解磁场在星星形成中的作用方面会有重大进展。更广泛的影响：这里提出的研究在星星形成研究的多个领域都有更广泛的影响。这种影响的例子有：改进了用于大尺度结构形成和星系演化模拟的星星形成方法;改进了基于维里定理的分子云质量估计（其中磁压通常被忽略）;改进了对磁场在年轻恒星甚至活动星系核产生双极风中的作用的理解。该项目还将有助于加强研究和教育基础设施，特别是阿尔马设施和仪器。使用合成成像阵列的偏振测量有许多潜在的缺陷，而阿尔马的目标是充分发挥其偏振映射能力。该小组将成为阿尔马的首批用户之一，并将带来其在干涉偏振测量方面的专业知识和经验，以便阿尔马能够尽早以最佳方式进行偏振科学。这将包括参与阿尔马硬件调试和测试用于偏振成像的阿尔马软件，并向科学界提供建模代码，以便所有用户都可以充分利用阿尔马偏振映射的结果。此外，一名研究生将接受观察和分析技术方面的培训。随着阿尔马在不久的将来上线，学生在与阿尔马研究相关的领域接受培训至关重要。首席研究员有培训学生在无线电偏振测量的历史，并将继续培训博士生谁将能够充分利用阿尔马。