Probing The High Redshift Universe with the NGST
  Through a combination of deep wide-field imaging and multi-object spectroscopy, the Next Generation Space Telescope will be able to chart with unprecedented accuracy the evolution of cosmic structures after the `dark ages' (z<5), when galaxies are thought to assemble and form the bulk of their stars. In this talk I will discuss how NGST observations might determine the history of the stellar birthrate in the universe and reveal the character of cosmological ionizing sources at high redshifts. 
Piero Madau (STScI)