Collaborative Research: Spectral diagnostics of heavy elements at high redshift

AST-1109061/1108830费兰/库尔卡尼重元素是恒星演化过程中产生的元素，然后分布到星际空间。因此，了解星系的丰富历史对于理解恒星形成和反馈过程至关重要，这些过程是星系演化的核心。背景类星体或伽马射线暴余辉光谱中的衰减Lyman-α(DLA)和亚DLA吸收谱线为测量遥远星系的重元素含量提供了最灵敏的工具。高分辨率光谱学揭示了一些有趣的谜题，特别是与金属度和富集度的变化有关。目前和拟议中的大型望远镜将极大地扩展观测数据库，特别是在高红移的情况下，但不幸的是，对于元素周期表中除镁以外的大多数元素来说，基本的原子数据--振子强度和复合系数--都高度不确定或未知。现有原子数据库中的这些空白是从光谱中获得丰度和实现观测的科学潜力方面的最大弱点。本项目将通过执行以下步骤来改善这种情况：1)使用最先进的量子程序计算所有相关离子从铝到锌的跃迁的更准确的振子强度；2)计算关键元素所有相关离子的双电子复合系数；3)将这些数据纳入广泛使用的光电离程序‘Cloudy’；4)将新的‘Cloudy’模型应用于现有和新的光谱数据；5)从观测和模拟结果向原子理论提供反馈(最后也是最关键的一步)。这项研究将有助于确定当前星系化学演化的图景是否准确，同时在原子数据和光电离模拟方面提供亟需的改进。由于该团队结合了原子物理、等离子体模拟和观测光谱学方面的专业知识，他们是唯一有资格进行这项工作的人。对广泛可用的建模工具“云”的改进将立即惠及从恒星形成云到活动星系核的其他天体物理学领域，因为这种工具被广泛使用，并每年被200多本出版物引用。这项工作包括这两个机构的重大教育收益和强有力的外联参与，并继续开展强有力的国际合作，初级研究人员将广泛接触到这一合作。由于团队的组成，在一个天文学家很少，特别是少数族裔或女性天文学家很少的地理区域，它还提高了科学工作者的素质和多样性。

AST-1109061/1108830Ferland/KulkarniHeavy elements are produced by stellar evolution and then distributed into interstellar space. Understanding the enrichment history of galaxies is therefore crucial to understanding the star formation and feedback processes that are central to galaxy evolution. Absorption lines of damped Lyman-alpha (DLA) and sub-DLA absorbers in the spectra of background quasars or gamma-ray burst afterglows provide the most sensitive tools to measure the heavy element content of distant galaxies. High-resolution spectroscopy has revealed some interesting puzzles, especially relating to variations in metallicities and enrichment. Current and proposed large telescopes will greatly expand the observational database, especially at high redshift, but unfortunately essential atomic data - both oscillator strengths and recombination coefficients - are highly uncertain or unknown for most elements beyond Magnesium in the periodic table. These gaps in the existing atomic database are the greatest weakness in deriving abundances from spectra and realizing the scientific potential of the observations. This project will improve that situation by carrying out the following steps: 1) calculate more accurate oscillator strengths for transitions of all relevant ions from Aluminum to Zinc using state-of-the-art quantal codes; 2) calculate dielectronic recombination coefficients for all relevant ions of key elements; 3) incorporate these data into the widely used photoionization code 'Cloudy'; 4) apply the new 'Cloudy' models to existing and new spectral data; and 5) provide feedback to the atomic theory from the observational and modeling results (the last and most crucial step).This study will help to determine whether the current picture of chemical evolution of galaxies is accurate, while providing a much-needed improvement in atomic data and photoionization modeling. Because the team combines expertise in atomic physics, plasma simulations, and observational spectroscopy, they are uniquely qualified to carry out this work.The improvements to the widely available modeling tool 'Cloudy' will be of immediate benefit to other areas of astrophysics ranging from star-forming clouds to active galactic nuclei, because that utility is used extensively and cited in over 200 publications each year. The work includes significant educational benefits at both institutions and a strong outreach involvement, and continues a strong international collaboration, to which the junior researchers will be extensively exposed. Due to the make-up of the team, it also enhances the quality and diversity of the scientific workforce in a geographical region with few astronomers, and especially very few minority or women astronomers.