  We present deep, high angular-resolution HST/NICMOS imaging in the Hubble
Deep Field South (HDF-S), focusing on a subset of 14 Distant Red Galaxies
(DRGs) at z ~ 2.5 galaxies that have been pre-selected to have J-K > 2.3. We
find a clear trend between the rest-frame optical sizes of these sources and
their luminosity-weighted stellar ages as inferred from their broad-band
spectral energy distributions (SEDs). Galaxies whose SEDs are consistent with
being dusty and actively star forming generally show extended morphologies in
the NICMOS images (r_e >~ 2 kpc), while the 5 sources which are not vigorously
forming stars are extremely compact (r_e <~ 1 kpc). This trend suggests a
direct link between the mean ages of the stars and the size and density of the
galaxies and supports the conjecture that early events quench star-formation
and leave compact remnants. Furthermore, the compact galaxies have stellar
surface mass densities which exceed those of local galaxies by more than an
order of magnitude. The existence of such massive dense galaxies presents a
problem for models of early-type galaxy formation and evolution. Larger samples
of DRGs and higher spatial resolution imaging will allow us to determine the
universality of the results presented here for a small sample.
