The Chemical Enrichment of the Local Universe

Abstract

Gas-phase chemical abundances are powerful probes of galactic evolutionary mechanisms: the Interstellar Medium is enriched with the products of stellar nucleosynthesis, diluted by pristine gas infall, and mixed by various processes on different timescales. A significant sample of chemical abundances offers insight into these processes and the products of star formation. This work has produced such a sample to study the chemical evolution of metal-poor, low-mass dwarf galaxies and metal-rich spiral galaxies. The chemical abundances in two such spirals, NGC 2403 and M33, reveal that these systems are chemically enriched from the inside out and have small dispersions about their abundance gradients. Electron temperature measurements in multiple ionization zones are required to accurately constrain the chemical abundance of an H II region, and it is shown that a lack of temperature data can significantly inflate the variation in O/H within a spiral galaxy. While local spirals provide the best laboratories to study chemical enrichment on small spatial scales, dwarf galaxies are more comparable to the highly star-forming, low-mass systems in the early universe. New UV spectroscopy of the dwarf galaxy Pox 186 enables a robust calculation of the C/O abundance, stellar population parameters, and ionizing conditions in a system analogous to those at high redshift. The measured C/O abundance suggests a star-formation history similar to other more massive dwarf galaxies; however, the observed very high-ionization emission features imply that the ionization conditions in Pox 186 and reionization-era galaxies are sensitive to the recent formation of very massive stars.