The enrichment of iron (Fe) relative to the alpha-elements such as oxygen and magnesium (Mg) is a way to measure the ages of quasi-stellar objects (QSOs) and to probe nucleosynthesis in the galaxy formation epoch. This works because QSOs exhibit prominent Fe II features and Mg II resonance doublet emission in the ultraviolet. However, one must determine how Fe II emission varies with physical condition before it can be used as an abundance indicator. The present researchers have previously developed the most sophisticated model iron atom currently available, partially supported by NSF award AST-0206150. Because this model is sensitive to the strong radiation field in QSOs, it allows for the strong effect of non-abundance factors such as micro-turbulence, ionizing flux, and hydrogen density, which must be considered before any accurate abundance can be derived. Combining these Fe II model results with multi-bandpass emission spectrum measurements, this project will assess the predictive capabilities of the model, and study the physical conditions, especially micro-turbulence, in the Broad Line Regions of nearby quasars. The project will also consider the effects on the deduced spectral energy distribution of the QSO in the ultraviolet, and on the measurement of Fe/Mg ratios.
The study is international and multi-disciplinary, combining leading theoretical, observational and experimental groups working on Fe II from the USA (modeling), Europe (spectroscopy), and Australia (observations). Since Fe II is important in many ionized plasmas, the project will have an impact on a wide range of astrophysical studies. Outreach work from the lead institution reaches a diverse population with a large number of under-represented groups.
