The high-redshift Universe with Spitzer
  When did galaxies start forming stars? What is the role of distant galaxies
in galaxy formation models and the epoch of reionization? What are the
conditions in typical star-forming galaxies at redshifts >~4? Why is galaxy
evolution dependent on environment? The Spitzer Space Telescope has been a
crucial tool for addressing these questions. Accurate knowledge of stellar
masses, ages and star formation rates requires measuring rest-frame optical
(and ultraviolet) light, which only Spitzer can probe at high redshifts for a
sufficiently large sample of typical galaxies. Many of these science goals are
the main science drivers for the James Webb Space Telescope, and Spitzer
afforded us their first exploration.
