KDC sizes versus the mass-weighted stellar ages inside r_KDC. The first panel shows the actual physical sizes of the KDCs, and the other two panels show their relative size r_KDC/r_eff. The stellar mass of the host galaxies at redshift z = 0 for the first two panels and the age difference between stars inside and outside r_KDC (inner minus outer) for the last panel are color coded.