We present a study of the size growth of the red sequence between 0.5<z<3, tracing the evolution of quiescent galaxies in both effective half-light and half-mass radii using multi-wavelength JWST/NIRCam imaging provided by the PRIMER survey. Half-light radii are measured from imaging in 6 different filters for 455 quiescent galaxies with log(M_/M_⊙)>10, whereas half-mass radii are derived from the F444W profiles together with the F277W-F444W color-M_/L relation. We investigate the dependence of the ratio r_e, mass/r_e, light on redshift, stellar mass, and the wavelength used to measure r_e, light, also separating the sample into younger and older quiescent galaxies. Our data demonstrate that rest-frame infrared sizes accurately trace mass-weighted sizes while sizes measured at rest-frame optical wavelengths (0.5-0.7μm) are 0.1-0.2 dex larger, with only minor variations in redshift. We find that the average size of young quiescent galaxies agrees with that of old quiescent galaxies at intermediate masses, 10<log(M_*/M_⊙)<11, within their respective uncertainties in all observed-frame half-light, rest-frame half-light and half-mass radius measurements. At face value, our results point to a combination of progenitor bias and minor mergers driving the size growth of intermediate-mass quiescent galaxies at 0.5<z<3. Our results further indicate that the varying contributions to the general quiescent population by young and old quiescent galaxies can mimic evolution in redshift.
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