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Abstract We study the relationship between the morphology and star formation history (SFH) of 361 quiescent galaxies (QGs) at redshift 〈 z obs 〉 ≈ 2, with stellar mass log M * ≥ 10.3 , selected with the UVJ technique. Taking advantage of panchromatic photometry covering the rest-frame UV-to-NIR spectral range ( ≈40 bands), we reconstruct the nonparametric SFH of the galaxies with the fully Bayesian SED fitting code P rospector . We find that the half-light radius R e , observed at z obs , depends on the formation redshift of the galaxies, z form , and that this relationship depends on M * . At log M * 11 , the relationship is consistent with R e ∝ 1 + z form − 1 , in line with the expectation that the galaxies’ central density depends on the cosmic density at the time of their formation, i.e., the “progenitor effect.” At log M * > 11 , the relationship between R e and z form flattens, suggesting that mergers become increasingly important for the size growth of more massive galaxies after they quenched. We also find that the relationship between z form and galaxy compactness similarly depends on M * . While no clear trend is observed for QGs with log M * > 11 , lower-mass QGs that formed earlier, i.e., with larger z form , have larger central stellar-mass surface densities, both within the R e (Σ e ) and central 1 kpc (Σ 1 kpc ), and also larger M 1 kpc / M * , the fractional mass within the central 1 kpc. These trends between z form and compactness, however, essentially disappear if the progenitor effect is removed by normalizing the stellar density with the cosmic density at z form . Our findings highlight the importance of reconstructing the SFH of galaxies before attempting to infer their intrinsic structural evolution.
Ji et al. (Mon,) studied this question.