The Evolution of Half-mass Radii and Color Gradients for Young and Old Quiescent Galaxies at 0.5 < z < 3 with JWST/PRIMER

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 multiwavelength JWST/NIRCam imaging provided by the PRIMER survey. Half-light radii are measured from imaging in six different filters for 502 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 re,mass/re,light on redshift, stellar mass, and the wavelength used to measure re,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 (0.5-0.7 μm) 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 observedframe 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.