Emission-Line Diagnostics of Galaxy Evolution with NGST
As a byproduct of its search for the first star forming galaxies, NGST will obtain high-quality spectra for thousands of galaxies in the redshift range z = 0 - 6 and beyond. Most of the galaxies will possess strong emission-line spectra, and these spectra will provide a wealth of information on their star formation rates, reddening, metal abundances, internal kinematics, and nuclear activity. This will make it possible to construct a comprehensive picture of the buildup of stars, metals, dust, and the nuclei of galaxies with cosmological lookback time. This paper reviews what can be learned from the spectra of distant emission-line galaxies. Simulations of NGST spectra are used to explore the instrumental tradeoffss for these applications, and the respective roles of NGST and groundbased surveys.