Letter to the Editor

Color profiles of disk galaxies at z = 1–3 observed with JWST: Implications for outer-disk formation histories

¹ Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), UTIAS, Tokyo Institutes for Advanced Study, University of Tokyo, Chiba, 277-8583, Japan
² Department of Astronomy, Peking University, 5 Yiheyuan Road, Haidian District, Beijing, 100871, China
³ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing, 100871, PR China
⁴ Center for Data-Driven Discovery, Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba, 277-8583, Japan
⁵ Department of Astronomy, Xiamen University, Xiamen, Fujian, 361005, PR China
⁶ School of Astronomy and Space Science, University of Chinese Academy of Sciences (UCAS), Beijing, 100049, China
⁷ Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, 113-0033, Japan

^⋆ Corresponding authors; si-yue.yu@ipmu.jp, dwxu.astro@gmail.com

Received: 25 October 2024
Accepted: 17 December 2024

Abstract

We investigate the deconvolved color profiles of 223 disk galaxies at redshifts of z = 1–3 observed by the James Webb Space Telescope (JWST) as part of the Cosmic Evolution Early Release Science survey (CEERS). The filters were selected to approximate the rest-frame B − Y color, which is used to identify U-shaped color profiles –those becoming progressively bluer with increasing radius, then turning redder beyond a specific point. We find that 36% of Type II (down-bending) disks exhibit U-shaped color profiles with a minimum at or near the disk break. In contrast, no Type I (single-exponential) disks and only 9% of Type III (up-bending) disks show such a profile. The presence of U-shaped color profiles in Type II disks likely arises from the interplay between a star-formation threshold and spiral- or bar-driven secular radial migration of older stars outward. The fraction of Type II disks exhibiting a U-shaped color profile remains almost consistent across two redshift bins, z = 1–2 and z = 2–3, but is significantly lower than that observed in the local Universe, likely because the secular process of radial migration at high redshift may not have had sufficient time to significantly influence the disk structure. The absence of U-shaped color profiles in Type II disks could point to rapid rather than secular radial star migration potentially caused by violent clump instabilities, transporting both younger and older stars to the outer disk. Our results provide useful constraints on the formation and evolution models of disk galaxies in the early Universe.