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 _* > 10¹⁰ 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.