Determining the chemical composition of galaxies is crucial for understanding their formation and evolution. Standard techniques, utilizing emission line spectra of the diffuse interstellar gas (specifically HII regions), is plagued by large and poorly understood systematic uncertainties. This project will develop a new, and potentially transformative, approach based on near-infrared spectroscopy of individual red supergiant stars. The output of these stars peaks in the J-band, where the spectra are rich in atomic lines. New multi-object infrared spectrographs on 10-meter-class telescopes will be able to obtain sufficient resolution to derive accurate abundances to distances of 10 megaparsecs. The purpose of this project is to develop, validate and exploit this new technique, in several steps: (1) The technique will be tested in the Milky Way and the Magellanic Clouds, against complementary techniques using HII region and blue supergiant star spectra; (2) Local Group galaxies of extremely low metallicity (NGC 3109, WLM, IC 1613) and the spirals M31 and M33 will be studied and compared with results from blue supergiants; (3) the technique will be applied to spiral galaxies beyond the Local Group out to a few megaparsecs (NGC 300, NGC 2403, M81). Accurate abundances and abundance gradients will be obtained, allowing constraints on the evolutionary states and histories of star forming galaxies, as well as an assessment of the reliability of H II region techniques. The method will also be extended to super-star clusters, which contain many dozens of red supergiants dominating the J-band flux, and which may be useful as cosmological abundance indicators at even larger distances. Eventually, this technique may be best exploited by the next generation of large telescopes, achieving abundance measurements out to 100 megaparsecs, a substantial volume of the local universe. The project will support the work of one graduate student, who will participate in international collaborations. Results will be incorporated into education and public outreach activities conducted by the Principal Investigator.
