Rest-Frame UV and Optical Structural Evolution of Narrowband-Selected Lyman-alpha Emitters at z = 2-7 with JWST/NIRCam

Abstract: We present a systematic study of the rest-frame ultraviolet (UV) and optical morphologies of Ly$α$ emitters (LAEs) at $z \simeq 2$-$7$ from the SILVERRUSH multi-narrowband catalog, using JWST/NIRCam imaging from COSMOS-Web. We fit Sérsic profiles in four NIRCam filters (F115W, F150W, F277W, F444W) for LAEs spanning $\sim 2.2$ Gyr of cosmic time. LAE sizes show a mild increase from rest-frame UV to optical wavelengths, with a median optical-to-UV size ratio of $$R_{e,\rm opt}/R_{e,\rm UV} = 1.14<sup>{+0.01}_{-0.02}$$, indicating a small morphological $K$-correction; this offset is significant at $z \leq 5.7$ but not at $z = 6.6$. The rest-frame optical sizes follow a power-law evolution, given by $R_e \propto (1+z)^{-0.94 \pm 0.09}$, decreasing from $0.91<sup>{+0.07}_{-0.07}$ kpc at $z = 2.2$ to $\sim 0.5$ kpc at $z \gtrsim 5$, in close agreement with a recent JWST study of spectroscopically confirmed LAEs. The rest-frame optical size-mass relation slopes are broadly consistent with those of the general star-forming galaxy (SFG) population, while LAEs lie below it in normalization over $z \sim 3$-$6$. More compact LAEs tend to exhibit higher Ly$α$ equivalent widths, a trend driven mainly by the most compact, marginally resolved sources. These compact systems also occupy elevated SFR surface-density regimes, consistent with a scenario in which concentrated star formation may facilitate Ly$α$ escape. No significant correlation of LAE rest-frame optical size with projected large-scale environment is found over $z \simeq 2$-$7$, suggesting that LAE morphology may be governed primarily by internal galaxy properties, except possibly in the most extreme overdensities.