Spectro-Photometric Constraints on Galaxy Evolution with NGST

The Next Generation Space Telescope (NGST) will gather unprecedented spectro-photometric data on galaxies out to the highest redshifts. It is therefore crucial to identify the spectro-photometric diagnostics within reach of NGST, which will allow us to best constrain the history of star formation and evolution of galaxies. The primary parameters to be determined are the ongoing rate of star formation and stellar mass of galaxies at all redshifts. In this context, we briefly review the reliability of various star formation rate and mass estimators of galaxies in a full range of redshifts, with particular emphasis on the relative merits of optical versus near- to mid-IR observations.