Heavy 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.
