JWST Unveils the Bimodal Nature of Lyα Emitters at 3 &lt; <i>z</i> &lt; 7: Pristine versus Merger-driven Populations

Abstract We present a systematic study of merging galaxies among Lyα emitters (LAEs) using James Webb Space Telescope/NIRCam high-resolution imaging data. From a large sample of 817 spectroscopically confirmed LAEs at 3 &lt; z &lt; 7 in the GOODS-S field, we identify late-stage mergers and interacting systems (late-stage mergers and galaxy pairs) with fractions of 39.4% ± 2.5% and 60.6% ± 6.3%, respectively. The late-stage merger fraction increases from ∼15% at z &gt; 6 to 45%–50% at z = 3, while the interaction fraction rises from ∼45% at z &gt; 6 to 70% at z &lt; 4. These fractions exhibit significant redshift evolution and depend on both stellar mass ( M * ) and UV magnitude ( M UV ), being most prevalent in massive ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⋆</mml:mo> </mml:msub> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>&gt;</mml:mo> <mml:mn>8.5</mml:mn> </mml:math> ) and bright ( M UV &lt; −19.5) systems. At fixed M * and M UV , we find negligible differences in the UV slope ( β ) between late-stage mergers and isolated LAEs; however, a clear bimodal distribution emerges in the solar mass–specific star formation rate ( M * –sSFR) plane. Our results suggest the presence of two evolutionary classes: pristine LAEs, low-mass ( M * &lt; 10 8.5 M ⊙ ), isolated systems that likely represent early-stage galaxies with minimal merger activity; and merger-driven LAEs, massive ( M * &gt; 10 8.5 M ⊙ ) systems in which galaxy interactions may enhance star formation and/or facilitate the escape of Lyα photons, or involve mergers with less evolved LAE companions. These findings are consistent with existing observational and theoretical studies, and indicate that galaxy mergers can play an important, though not ubiquitous, role in shaping the evolution and observability of LAEs during the first 2 billion years of cosmic history.