Structural evolution of quiescent galaxies at intermediate redshift at UV and red rest-frame wavelengths

We model the wavelength dependence of structural parameters for a mass-limited sample (M_>10¹⁰M_) of ~27,000 quiescent galaxies with $0.2 < z < 0.6$ using $grizy$ photometry from Subaru/Hyper Suprime-Cam and dense spectroscopy from the HectoMAP survey. Based on Sérsic profile fits in all five bands, we estimate the circularized half-light radius Re,c and Sérsic index n in two rest-frames: UV (3500 Å) and red (7000 Å). Combined with M_, z, and Dₙ4000, Re,c and n enable exploration of the evolution in the structural properties - stellar mass correlations for quiescent galaxies with different stellar population ages. At intermediate redshift, quiescent galaxies at all stellar masses show a systematic decline in Re,c and rise in n with rest-frame wavelength. These structural variations are stronger for galaxies that recently joined the quiescent population (newcomers) than for the descendants of galaxies that are already quiescent at the survey limit, z ~ 0.6 (aging population). The combined evidence supports inside-out quenching as the dominant mechanism halting star formation during this epoch. The typical size of a M_~10¹¹M_ quiescent galaxy increases by ~30% between z ~ 0.6 and z ~ 0.2 in the red and remains constant in the UV; newcomers are ~20% larger than the aging population. In the UV, quiescent galaxies maintain a constant n~4 for the aging population and n~2 for newcomers; in the red, both subpopulations have de Vaucouleurs profiles. Our findings link newcomers to their direct progenitors in the star-forming population. For the aging population, we suggest minor mergers with progressively redder satellites at lower redshifts as the primary driver of quiescent galaxy evolution. Forthcoming sensitive large-area imaging surveys will allow testing this prediction.