The JWST Unveils the Bimodal Nature of Lyman Alpha Emitters at 3 <z<7: Pristine versus Merger-Driven Populations

Abstract

We present a systematic study of merging galaxies among Lyman-alpha emitters (LAEs) using JWST/NIRCam high-resolution imaging data. From a large sample of 817 spectroscopically confirmed LAEs at $3<z<7$ in the GOODS-S field, we identify late-stage mergers and interacting systems with fractions of $39.4\%\pm2.5\%$ and $60.6\%\pm6.3\%$, respectively. These fractions exhibit significant redshift evolution and depend on both stellar mass ($M_*$) and UV magnitude ($M_{\rm UV}$), being most prevalent in massive ($\log(M_*/M_\odot)>8.5$) and bright ($M_{\rm UV}<-19.5$) systems. At fixed $M_*$ and $M_{\rm UV}$, we find negligible differences in the UV slope ($\beta$) between late-stage mergers and isolated LAEs; however, a clear bimodal distribution emerges in the $M_*$-sSFR plane, where isolated LAEs peak at $\log(M_*/M_\odot)\approx7.8$ and $\log({\rm sSFR/yr^{-1}})\approx-7.4$, and late-stage mergers peak at $\log(M_*/M_\odot)\approx8.6$ and $\log({\rm sSFR/yr^{-1}})\approx-7.6$. Our results reveal two evolutionary classes -- Pristine LAEs, low-mass ($M_*<10^{8.5}M_\odot$), isolated systems that represent early-stage galaxies with minimal merger interactions, and Merger-driven LAEs, massive ($M_*>10^{8.5}M_\odot$) systems in which mergers enhance star formation and facilitate the escape of Lyman-alpha photons or accrete pristine LAEs -- both of which are consistent with both observational and theoretical expectations and collectively demonstrate that mergers are a central driver of LAE evolution across the first two billion years.