2026ApJ...997..126S

Understanding the morphological structures of Lyα emitters (LAEs) is crucial for unveiling their formation pathways and the physical origins of Lyα emission. However, the evolution of their sizes and structural scaling relations remains debated. In this study, we analyze a large sample of 876 spectroscopically confirmed LAEs at 3 ≲ z < 7, selected from the MUSE, VANDELS, and CANDELSz7 surveys in the GOODS-S, Ultra Deep Survey, and COSMOS fields. Utilizing James Webb Space Telescope NIRCam imaging data, we measure their rest-frame UV and optical V-band effective radii (R_e) through two-dimensional Sérsic profile fitting. Our results show that these LAEs are generally compact, with a median R_e,UV of 0.50${}_{-0.24}^{+0.30}$ kpc and a median R_e,V of 0.57${}_{-0.24}^{+0.33}$ kpc. The size evolution follows R_e,UV ∝ (1 + z)^{–0.91±0.10} and R_e,V ∝ (1 + z)^{–0.93±0.18}, respectively. Their UV and optical sizes are statistically comparable, indicating negligible UV-to-optical color gradients. For the first time, we establish the rest-frame optical size-mass relation for LAEs at z > 3, finding slopes comparable to typical star-forming galaxies, but with slightly smaller sizes at a given stellar mass. These results provide important clues for understanding the structural evolution of LAEs in the early Universe.