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 Wide Field Camera 3 (WFC3) on the Hubble Space Telescope to determine YHVz color-color-selection criteria to identify and characterize 1.5 < z < 3.5 galaxies in the Hubble Ultra Deep Field 2009 (HUDF09) and Early Release Science (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 similar to 25% of both intermediate and high mass galaxies, i.e., above 10(10) M-circle dot. 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) M-circle dot. 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 (similar to 25%) of smooth spheroids, are evident above 10(11) M-circle dot. Strikingly, by 1.5 < z < 2.25 roughly two out of every three galaxies at the highest masses are spheroids. In our small sample, the fraction of star-forming galaxies at these mass scales decreases concurrently from similar to 60% to similar to 5%. If confirmed, this indicates that z similar to 2 is the epoch of both the morphological transformation and quenching of star formation which assemble the first substantial population of massive ellipticals.