The Collective Voice of Ly$\alpha$ Emitters: Insights from JWST Stacked Spectroscopy

Abstract

We present a spatially resolved stacked analysis of 287 LAEs at $z>4$ observed with JWST/NIRSpec prism spectroscopy. By constructing a two-dimensional stack from public surveys (CAPERS, CEERS, JADES, and RUBIES), we probe the average internal structure of typical LAEs on sub-kiloparsec scales. We find a clear radial decoupling between resonant and non-resonant emission: while EW(H$\beta$) and other optical lines decline with radius, EW(Ly$\alpha$) increases toward the outskirts, and the Ly$\alpha$ escape fraction rises from $\sim 16\%$ in the center to $\gtrsim 24\%$ at larger radii. This behavior suggests that resonant scattering redistributes Ly$\alpha$ photons into lower-density outer regions, where escape becomes more efficient. Optical diagnostics and $T_e$ measurements reveal low metallicities ($12+\log (O/H)\simeq 7.7\pm 0.2$), high ionization parameters, negligible dust attenuation, and systematically elevated N/O ratios ($\log (N/O)\sim -0.4$). The latter place typical LAEs among the growing population of nitrogen-enhanced high-redshift galaxies, pointing to rapid and possibly feedback-driven chemical enrichment. The inferred ionizing photon production efficiency, $\log ({\xi }_{\mathrm{ion}}/\mathrm{Hz}\mathrm{er}{\mathrm{g}}^{-1})\simeq 25.1-25.2$, together with the high Ly$\alpha$ escape fractions, suggests that these systems are efficient, though not extreme, contributors to the ionizing photon budget. Comparison with SPICE radiation-hydrodynamic simulations shows that bursty supernova feedback models naturally reproduce the observed radial trends in Ly$\alpha$ escape, UV slope, and emission-line equivalent widths, linking the spatial redistribution of Ly$\alpha$ to stochastic star formation and feedback-driven gas flows. Our results demonstrate that Ly$\alpha$ emission, chemical enrichment, and feedback are tightly connected in typical $z>4$ LAEs. (Shortened version for arXiv)

22 pages, 9 main figures, 2 main tables; 4 appendixes. Accepted for publication in A&A