The Size Evolution and the Size-Mass Relation of Lyman-Alpha Emitters across $3 \lesssim z < 7$ as Observed by JWST
Qi Song, F. S. Liu, Jian Ren, Pinsong Zhao, Qifan Cui, Yubin Li, Hao Mo, Yuchong Luo, Guanghuan Wang, Nan Li, Hassen M. Yesuf, Weichen Wang, Xin Zhang, Xianmin Meng, Mingxiang Fu, Bingqing Zhang, Chenxiaoji Ling
TL;DR
This study targets the size evolution and size–mass scaling of Lyman-alpha emitters (LAEs) across $3 \lesssim z < 7$ using JWST/NIRCam imaging to obtain rest-frame UV and optical effective radii via two-dimensional Sérsic fits. Leveraging a large, homogeneous sample of 876 spectroscopically confirmed LAEs from MUSE, VANDELS, and CANDELSz7 across GOODS-S, UDS, and COSMOS, the authors quantify compact morphologies with median $R_{\rm e,UV} \approx 0.50$ kpc and $R_{\rm e,V} \approx 0.57$ kpc, and find $R_{\rm e,UV} \propto (1+z)^{-0.91 \pm 0.10}$ and $R_{\rm e,V} \propto (1+z)^{-0.93 \pm 0.18}$. They report negligible UV-to-optical color gradients (UV and optical sizes are statistically comparable) and establish the rest-frame optical size–mass relation for LAEs at $z>3$, with slopes similar to typical star-forming galaxies but slightly smaller sizes at a given $M_*$. The results imply that LAEs maintain compact morphologies across the early universe and provide robust constraints on their structural evolution and connection to star-forming galaxies. Overall, the work demonstrates JWST’s power to unify size measurements across rest-frame wavelengths and redshift, enabling a clearer view of LAE formation pathways.
Abstract
Understanding the morphological structures of Lyman-alpha emitters (LAEs) is crucial for unveiling their formation pathways and the physical origins of Ly$α$ 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 $3 \lesssim z < 7$, selected from the MUSE, VANDELS, and CANDELSz7 surveys in the GOODS-S, UDS, and COSMOS fields. Utilizing James Webb Space Telescope (JWST) NIRCam imaging data, we measure their rest-frame UV and optical V-band effective radii ($R_{\rm e}$) through two-dimensional Sérsic profile fitting. Our results show that these LAEs are generally compact, with a median $R_{\rm e,UV}$ of 0.50$^{+0.30}_{-0.24}$ kpc and a median $R_{\rm e,V}$ of 0.57$^{+0.33}_{-0.24}$ kpc. The size evolution follows $R_{\rm e,UV} \propto (1 + z)^{-0.91 \pm 0.10}$ and $R_{\rm e,V} \propto (1 + z)^{-0.93 \pm 0.18}$, 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 (SFGs), but with slightly smaller sizes at a given stellar mass. These results provide important clues for understanding structural evolution of LAEs in the early universe.