COLLABORATIVE RESEARCH: Spectral Diagnostics of Heavy Elements At High Redshift

重元素由恒星演化产生，然后分布到星际空间。因此，了解星系的富集历史对于理解恒星形成和反馈过程至关重要，而恒星形成和反馈过程是星系演化的核心。背景类星体或伽玛射线暴余辉光谱中的阻尼Lyman-alpha （DLA）和次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，特别是与金属丰度和富集度的变化有关。目前和计划中的大型望远镜将极大地扩展观测数据库，特别是在高红移时，但不幸的是，基本的原子数据——振荡强度和复合系数——对于元素周期表中除镁以外的大多数元素来说都是高度不确定或未知的。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的最大弱点。本项目将通过以下步骤改善这种情况：1)使用最先进的量子代码计算更准确的振荡器强度，用于从铝到锌的所有相关离子的跃迁；2)计算各关键元素相关离子的介电复合系数；3)将这些数据合并到广泛使用的光电离代码“Cloudy”中；4)将新的“云”模式应用于现有和新的光谱数据；5)从观测和建模结果中为原子理论提供反馈（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像是否准确，同时为原子数据和光电离模型提供急需的改进。由于该团队结合了原子物理学、等离子体模拟和观测光谱学方面的专业知识，他们是唯一有资格开展这项工作的人。对广泛使用的建模工具“Cloudy”的改进将直接造福于天体物理学的其他领域，从恒星形成云到活动星系核，因为该工具被广泛使用，每年在200多份出版物中被引用。这项工作包括两个机构的重大教育效益和强有力的外展参与，并继续进行强有力的国际合作，初级研究人员将广泛接触。由于该团队的组成，它还提高了一个天文学家很少，特别是少数民族或女性天文学家很少的地理区域的科学劳动力的质量和多样性。

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.