Mergers Drive Structural Complexity but Not Starbursts in Lyman-$\alpha$ Emitters at $3 < z < 4$: A JWST Spatially Resolved View

TL;DR

This study uses JWST imaging to analyze high-redshift Ly$ ext{α}$ emitters, finding that mergers increase structural complexity without triggering starbursts, and may influence Ly$ ext{α}$ photon escape.

Contribution

First spatially resolved SED analysis of merging LAEs at $3<z<4$ using JWST data, revealing structural perturbations without starburst activity.

Findings

Mergers are minor or major but do not induce starbursts.

Systems lie on the star-forming main sequence.

Mergers cause internal structural and dust distribution changes.

Abstract

Recent observations with the James Webb Space Telescope (JWST) reveal that the merger fraction among Ly$\alpha$ emitters (LAEs) at redshifts $z > 3$ is significantly higher than previously estimated. In this study, we focus on three high signal-to-noise merging LAE systems at $3 < z < 4$, selected from the VLT/MUSE-Deep survey in the GOODS-S field. We combine new \textit{JWST}/NIRCam broadband and medium-band imaging with archival \textit{HST}/ACS data to perform spatially resolved spectral energy distribution (SED) fitting using the \textsc{Bagpipes} software package. Our analysis reveals that two of the systems are minor mergers, while the third is a major merger. The close agreement between spatially resolved and integrated stellar mass estimates indicates that recent star formation does not significantly outshine the light from older stellar populations in these systems. Moreover, both the individual components and the systems as a whole lie on the star-forming main sequence, further supporting the conclusion that these mergers have not yet triggered substantial starburst activity. Furthermore, we detect prominent color gradients and disturbed dust distributions in these merging systems, indicating that the mergers have already induced significant internal structural perturbations. These morphological and dust-related changes may facilitate the escape of Ly$\alpha$ photons -- potentially through mechanisms such as gas redistribution or a reduced covering fraction of neutral hydrogen -- thereby playing a key role in shaping the observed properties of LAEs.