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

TL;DR

This study uses JWST observations to analyze the color profiles of 223 high-redshift disk galaxies, revealing insights into their formation and evolution, especially regarding radial migration and star formation processes.

Contribution

It provides the first large sample analysis of color profiles at $z=1$-3$, linking color profile types to galaxy formation mechanisms and their evolution over cosmic time.

Findings

36% of Type II disks show U-shaped color profiles.

U-shaped profiles are less common at high redshift than locally.

Secular radial migration likely influences color profiles in early disk galaxies.

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.