Is galaxy disk formation driven by inside-out star formation?

The evolution of galaxy size across a range of redshifts offers insight into the physical processes involved in the build-up of disk galaxies over cosmic time. Galaxies transition from increasingly clumpy morphologies to large disk and spheroid morphologies around cosmic noon (z ~ 2), although the process through which this occurs is not well understood. In this study, we explore the theory of inside-out disk formation using high-resolution imaging from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey fields (CANDELS), and UVCANDELS from HST, and the Cosmic Evolution Early Release Science Survey (CEERS) from JWST to measure rest-frame UV and rest-frame optical half-light radii of galaxies in the Extended Groth Strip (EGS) field at 1.5 < z < 3.0. The rest-UV images trace the locations of the most recent star formation, while the rest-optical is more representative of the underlying older stellar population, and by comparing rest-UV and rest-optical sizes and colors we can understand how star formation propagates through the disk. Both before and after cosmic noon, we find evidence of inside-out disk formation with predominantly larger UV sizes than optical for the most massive disks, more significantly at higher redshift. However, we also observe that the majority of galaxies with clumpy morphologies (n < 0.5) at lower masses exhibit larger UV sizes than rest-optical because the star formation is distributed in multiple ex-situ star forming clumps or mergers.