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 high mass end, structural parameters of green galaxies are intermediate between red and blue galaxies in each stellar mass bin at z < 2, indicating 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 high-mass end implies that these galaxies will not appear to be significantly shrunk until they are completely quenched into red QGs. For the green galaxies at 0.5 < z < 1.5, a morphological transformation sequence of bulge buildup can be seen as they are gradually shut down their star formation activities, while a faster morphological transformation is verified for the green galaxies at 1.5 < z < 2.5.

The effect of the morphological quenching mechanism on star formation activity at 0.5 < z < 1.5 in 3D-HST/CANDELS

“…The A v is derived during the SED fitting with the FAST code. The acceptable agreement between SFR UV,corr and SFR UV+IR is confirmed by previous works (e.g., Rangel et al 2014;Fang et al 2018;Gu et al 2019Gu et al , 2020.…”

“…Utilizing galaxies at 0.1 < z < 0.2 from the Galaxy and Mass As-sembly (GAMA) survey, Phillipps et al (2019) derive that the evolutionary time-scales of typical low-redshift galaxies from the BC through the GV to the RS are about 2-4 Gyr. In contrast, Pandya et al (2017) place an observational upper limit on the average population transition time-scale as a function of redshift, finding that galaxy quenching is on a fast track at high redshift, whereas it is on a slow track at low redshift, which is also consistent with the results from Gu et al (2019). Note that the quenching should be correlated with the morphology of the galaxy, if the quenching mechanism involves the reorganization of the stellar component of the galaxy via compaction events or dissipative mergers (Dekel et al 2009; Barro et al 2013Barro et al , 2017Wellons et al 2015) or a natural consequence of 'inside-out' growth combined with disk fading (e.g., Lilly & Carollo 2016).…”

“…Recently, on the basis of the CO(J =1-0) observation of nearby (z < 0.05) GV galaxies, Koyama et al (2019) assess the effects of GV galaxy morphologies (i.e., disk-and bulge-dominated GV galaxies) on the efficiency of star formation, and find that the emergence of the stellar bulge does not decrease the efficiency of ongoing star formation, which contrasts with the prediction of the MQ (e.g., Martig et al 2009;Bluck et al 2014). But conceivably, the MQ could be even more important at high redshift, which results from the fact that the RS is already in place (e.g., Gu et al 2018Gu et al , 2019, and the gas fraction in ETGs might be higher owing to the higher gas infall rates and the greater presence of unvirialized clusters (e.g., Bell et al 2004;Cirasuolo et al 2007). Therefore, it is still desirable to assess the effects of galaxy morphologies on the star formation quenching at higher redshift.…”

“…The nonparametric parameter refers to the concentration index (C), which can describe the concentration of the surface brightness distribution of a galaxy. Many previous works have tested and adopted this measurement (Kong et al 2009;Wang et al 2012;Fang et al 2015;Gu et al 2018Gu et al , 2019Lu et al 2020). The nonparametric measurements are sensitive to the signal-to-noise ratio (S/N) per pixel, especially for S/N 2 (Lotz et al 2004;Lisker 2008), while one of our selection criteria, use phot=1, can ensure that our measurements are performed on a reliable detection in the H F160W (see section 2.3).…”

Morphological Transformation and Star Formation Quenching of Massive Galaxies at 0.5 < z < 2.5 in 3D-HST/CANDELS

“…The massive (log M * /M ≥ 10) galaxies can be classified into blue, green and red populations according to the dust-corrected colors out to z = 2.5 (see Wang et al 2017;Gu et al 2018 for detail). We have calculated the average quenching timescale as a function of redshift (Gu et al 2019), which is denoted by the red line in Figure 13. The result explicitly indicates that the quenching process happens in a shorter timescale at high redshifts, and the timescale becomes longer with decreasing redshifts, which is in a good agreement with previous works (Barro et al 2013;Pandya et al 2017).…”