CANDELS: Correlations of SEDs and Morphologies with Star-formation
  Status for Massive Galaxies at z ~ 2
  We present a study on Spectral Energy Distributions, Morphologies, and star
formation for an IRAC-selected extremely red object sample in the GOODS Chandra
Deep Field-South. This work was enabled by new HST/WFC3 near-IR imaging from
the CANDELS survey as well as the deepest available X-ray data from Chandra 4
Ms observations. This sample consists of 133 objects with the 3.6um limiting
magnitude of [3.6] = 21.5, and is approximately complete for galaxies with M
>10^{11}M_sun at 1.5 < z < 2.5. We classify this sample into two types,
quiescent and star-forming galaxies, in the observed infrared color-color
([3.6]-[24] vs K-[3.6]) diagram. The further morphological study of this sample
show a consistent result with the observed color classification. The classified
quiescent galaxies are bulge dominated and star-forming galaxies in the sample
have disk or irregular morphologies. Our observed infrared color classification
is also consistent with the rest-frame color (U-V vs V-J) classification. We
also found that quiescent and star-forming galaxies are well separated in the
nonparametric morphology parameter (Gini vs M_{20}) diagram measuring their
concentration and clumpiness: quiescent galaxies have Gini coefficient higher
than 0.58 and star forming galaxies have Gini coefficient lower that 0.58. We
argue that the star formation quenching process must lead to or be accompanied
by the increasing galaxy concentration. One prominent morphological feature of
this sample is that disks are commonly seen in this massive galaxy sample at
1.5 < z < 2.5: 30% of quiescent galaxies and 70% of star forming galaxies with
M >10^{11}M_sun have disks in their rest-frame optical morphologies. The
prevalence of these extended, relatively undisturbed disks challenges the
merging scenario as the main mode of massive galaxy formation.
