Early JWST imaging reveals strong optical and NIR color gradients in galaxies at $z\sim2$ driven mostly by dust

TL;DR

This study uses early JWST imaging to analyze color gradients in galaxies at z~2, revealing that most are driven by dust attenuation, with some showing signs of centrally concentrated star formation, demonstrating JWST's capability for detailed galaxy analysis.

Contribution

First application of JWST NIRCam imaging to resolve and analyze color gradients in galaxies at cosmic noon, distinguishing dust effects from stellar age variations.

Findings

Most star-forming galaxies have dust-driven negative color gradients.

Approximately 15% of star-forming galaxies show signs of central star formation.

Quiescent galaxies exhibit diverse UVJ color profiles, with some indicating central star formation.

Abstract

Recent studies have shown that galaxies at cosmic noon are redder in the center and bluer in the outskirts, mirroring results in the local universe. These color gradients could be caused by either gradients in the stellar age or dust opacity; however, distinguishing between these two causes is impossible with rest-frame optical photometry alone. Here we investigate the underlying causes of the gradients from spatially-resolved rest-frame $U-V$ vs. $V-J$ color-color diagrams, measured from early observations with the James Webb Space Telescope. We use $1\, \mu m - 4\, \mu m$ NIRCam photometry from the CEERS survey of a sample of 54 galaxies with $M_* / M_\odot>10$ at redshifts $1.7<z<2.3$ selected from the 3D-HST catalog. We model the light profiles in the F115W, F200W and F356W NIRCam bands using \texttt{imcascade}, a Bayesian implementation of the Multi-Gaussian expansion (MGE) technique which flexibly represents galaxy profiles using a series of Gaussians. We construct resolved rest-frame $U-V$ and $V-J$ color profiles. The majority of star-forming galaxies have negative gradients (i.e. redder in the center, bluer in the outskirts) in both $U-V$ and $V-J$ colors consistent with radially decreasing dust attenuation. A smaller population (roughly 15\%) of star-forming galaxies have positive $U-V$ but negative $V-J$ gradients implying centrally concentrated star-formation. For quiescent galaxies we find a diversity of UVJ color profiles, with roughly one-third showing star-formation in their center. This study showcases the potential of JWST to study the resolved stellar populations of galaxies at cosmic noon.