The Mass Dependence of Structure, Star Formation Rate, and Mass Assembly Mode at 0.5 < z < 2.5

Abstract

To investigate the mass dependence of structural transformation and star formation quenching, we construct three galaxy samples using massive ( M *  > 10 10 M ⊙ ) red, green, and blue galaxy populations at 0.5 <  z  < 2.5 in five 3D– HST /CANDELS fields. The structural parameters, including effective radius ( r e ), galaxy compactness (Σ 1.5 ), and second-order moment of 20% brightest pixels ( M 20 ), are found to be correlated with stellar mass. Sérsic index ( n ), concentration ( C ), and Gini coefficient ( G ) seem to be insensitive to stellar mass. The morphological distinction between blue and red galaxies is found at a fixed mass bin, suggesting that quenching processes should be accompanied with transformations of galaxy structure and morphology. Except for r e and Σ 1.5 at the high-mass end, structural parameters of green galaxies are intermediate between red and blue galaxies in each stellar mass bin at z  < 2, indicating that green galaxies are at a transitional phase when blue galaxies are being quenched into quiescent statuses. The similar sizes and compactness for the blue and green galaxies at the high-mass end imply that some of these galaxies will not appear to be significantly shrunk until they are completely quenched into red quiescent galaxies. For the green galaxies at 0.5 <  z  < 1.5, a morphological transformation sequence of bulge buildup can be seen as their star formation activities are gradually shut down, while a faster morphological transformation is verified for the green galaxies at 1.5 <  z  < 2.5.