Dissecting galaxies with bright stars and HII regions

University Of Hawaii, Honolulu

Investigators

Abstract

This project addresses two long-standing issues concerning the distances and chemical abundances of galaxies: first, the need for a distance indicator that is insensitive to both patchy interstellar dust and to variations in chemical abundances within a galaxy; and second, the need for a better method to infer the chemical compositions of galaxies from the spectra of star forming regions. The PI and co-PI will develop the flux-weighted gravity-luminosity relation (FGLR) technique, through which spectral class B and A supergiant stars can be used as "standard candles" in distance measurements. The techniques employs optical spectroscopy to obtain individual surface gravities, metallicities, temperatures, and thereby luminosities of these stars. They will calibrate this method with observations of the Magellanic Clouds, M31, and IC1316 . With subsequent spectroscopy of supergiant stars and HII regions in an additional sample of target galaxies, they will constrain the evolutionary states of star-forming galaxies from accurate stellar and nebular abundances, study radial abundance gradients in spiral galaxies, and characterize the effect of metallicity on other important techniques used in the extragalactic distance scale. The spectroscopic work rests on a library of detailed model stellar atmospheres, which they will improve and make publicly available. The work will inform strategies appropriate for upcoming generations of large telescopes. A postdoctoral researcher will be supported and mentored under this grant.