Active and passive galaxies at z~2: Rest-frame optical morphologies with
  WFC3
  We use the high angular resolution in the near-infrared of the WFC3 on HST to
determine YHVz color-color selection criteria to identify and characterize
1.5<z<3.5 galaxies in the HUDF09 and ERS (GOODS-South) fields. The WFC3 NIR
images reveal galaxies at these redshifts that were undetected in the
rest-frame UV HUDF/GOODS images, as well as true centers and regular disks in
galaxies classified as highly irregular in rest-frame UV light. Across the
1.5<z<2.15 redshift range, regular disks are unveiled in the WFC3 images of
~25% of both intermediate and high mass galaxies, i.e., above 10^10 Msun.
Meanwhile, galaxies maintaining diffuse and/or irregular morphologies in the
rest-frame optical light---i.e., not yet dynamically settled---at these epochs
are almost entirely restricted to masses below 10^11 Msun. In contrast at 2.25
< z < 3.5 these diffuse and/or irregular structures overwhelmingly dominate the
morphological mix in both the intermediate and high mass regimes, while no
regular disks, and only a small fraction (25%) of smooth spheroids, are evident
above 10^11 Msun. Strikingly, by 1.5 < z < 2.25 roughly 2 out of every 3
galaxies at the highest masses are spheroids. In our small sample, the fraction
of star-forming galaxies at these mass scales decreases concurrently from ~60%
to ~5%. If confirmed, this indicates that z~2 is the epoch of both the
morphological transformation and quenching of star-formation which assemble the
first substantial population of massive ellipticals.
