Measuring Chemical Abundances in Extragalactic Metal-Rich H II Regions


The analysis of metal-rich Hii regions has a profound impact on the calibration of abundance diagnostics widely used to measure the chemical content of star-forming galaxies, both locally and at high redshift. I review the main difficulties that affect direct abundance determinations from temperature-sensitive collisionally excited lines, and briefly discuss strong-line methods, in particular their empirical calibration. In the near future it will be possible to calibrate strong-line methods using metal recombination lines, providing abundances that are virtually insensitive to uncertainties on the nebular temperature structure. 1. Chemical abundances of metal-rich H II regions: why? Ionized nebulae (Hii regions) trace the sites of massive star formation in spiral and irregular galaxies. The rapid evolution of these stars, ending in supernovae explosions, and the subsequent recycling of nucleosynthesis products into the interstellar medium, make Hii regions essential probes of the present-day chemical composition of star-forming galaxies across the Universe. The study of nebular abundances is therefore crucial for understanding the chemical evolution of galaxies. In the following pages I will provide an optical astronomer’s perspective on some of the issues concerning the measuremen

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