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Observational evidence has been mounting over the past decade that at leastsome luminous (~2 L*) galaxies have formed nearly all of their stars within ashort period of time only 1-2x10^9 years after the Big Bang. These are examplesof the first major episodes of star formation in the Universe and provideinsights into the formation of the earliest massive galaxies. We have examinedin detail the stellar populations of six z~1.5 galaxies that appear to bepassively evolving, using both ground and space-based photometry coveringrest-frame UV to visible wavelengths. In addition, we have obtainedmedium-resolution spectroscopy for five of the six galaxies, covering therest-frame UV portion of the spectrum. Spectral synthesis modeling for four ofthese galaxies favors a single burst of star formation more than 1 Gyr beforethe observed epoch. The other two exhibit slightly younger ages with a higherdust content and evidence for a small contribution from either recent starformation or active nuclei. The implied formation redshifts for the oldest ofthese sources are consistent with previous studies of passive galaxies at highredshift, and improved stellar modeling has shown these results to be quiterobust. It now seems clear that any valid galaxy formation scenario must beable to account for these massive (2x10^11 M_sun) galaxies at very early timesin the Universe.

Stellar Populations of Luminous Evolved Galaxies at z~1.5