Abstract We present the UV-to-near-IR (NIR) size evolution of a sample of 161 quiescent galaxies with M * > 10 10 M ⊙ over 0.5 10 10.6 M ⊙ . To constrain the physical mechanisms driving the apparent size evolution, we study the relationship between R e and the formation redshift ( z form ) of quiescent galaxies. For lower-mass quiescent galaxies, this relationship is broadly consistent with R e ∝ ( 1 + z form ) − 1 , in line with the expectation of the progenitor effect. For higher-mass quiescent galaxies, the relationship between R e and z form depends on stellar age. Older quiescent galaxies have a steeper relationship between R e and z form than that expected from the progenitor effect alone, suggesting that mergers and/or post-quenching continuous gas accretion drive additional size growth in very massive systems. We find that the z > 3 quiescent galaxies in our sample are very compact, with mass surface densities Σ e ≳ 10 10 M ⊙ kpc −2 , and their R e are possibly even smaller than anticipated from the size evolution measured for lower-redshift quiescent galaxies. Finally, we take a close look at the structure of GS-9209, one of the earliest confirmed massive quiescent galaxies at z spec ∼ 4.7. From UV to NIR, GS-9209 becomes increasingly compact, and its light profile becomes more spheroidal, showing that the color gradient is already present in this earliest massive quiescent galaxy.
Ji et al. (Fri,) studied this question.