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 3.6 \mu m limiting magnitude of [ 3.6 ] = 21.5 , and is approximately complete for galaxies with M _ { * } > 10 ^ { 11 } M _ { \odot } at 1.5 \leq z \leq 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 \leq z \leq 2.5 : 30 % of quiescent galaxies and 70 % of star forming galaxies with M _ { * } > 10 ^ { 11 } M _ { \odot } 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 .