  My colleagues and I identified distant red galaxies (DRGs) with J-K>2.3 mag
in the GOODS-S field. These galaxies reside at z~1-3.5, (<z>=2.2) and based on
their ACS (0.4-1 micron), ISAAC (1-2.2 micron), and IRAC (3-8 micron)
photometry, they typically have inferred stellar masses > 10^11 solar masses.
Interestingly, more than 50% of these objects have 24 micron flux densities >50
micro-Jy. Attributing the IR emission to star-formation implies SFRs of
\~100-1000 solar masses per year. As a result, galaxies with stellar masses
>10^11 solar masses have specific SFRs equal to or exceeding the global value
at z~1.5-3. In contrast, galaxies with >10^11 solar masses z~0.3-0.75 have
specific SFRs less than the global average, and more than an order of magnitude
lower than that for massive DRGs at z~1.5-3. Thus, the bulk of star formation
in massive galaxies is largely complete by z~1.5. The red colors and large
inferred stellar masses in the DRGs suggest that much of the star formation in
these galaxies occurred at redshifts z>5-6. Using model star-formation
histories that match the DRG colors and stellar masses at z~2-3, and
measurements of the UV luminosity density at z>5-6, we consider what
constraints exist on the stellar initial mass function in the progenitors of
the massive DRGs at z~2-3.
