An Updated Characterization of Luminous Ly{\alpha} emitters at the End of Reionization

TL;DR

This study characterizes 14 luminous Lyα emitters at z≈6, revealing they are low-mass, young starburst galaxies with high Lyα escape fractions, contributing significantly to reionization.

Contribution

It provides a detailed multi-wavelength analysis that resolves previous mass overestimations and links high Lyα escape fractions to vigorous star formation in early dwarf galaxies.

Findings

Luminous LAEs are low-mass, ultra-young dwarf starbursts.

High Lyα escape fractions (median >40%) increase with bluer UV continua.

Internal dust, not neutral hydrogen, primarily suppresses Lyα radiative transfer.

Abstract

We present a multi-wavelength physical characterization of 14 luminous Ly$\alpha$ emitters (LAEs) at $z\approx6$, integrating deep ground-based Magellan/M2FS spectroscopy with heterogeneous JWST/NIRCam broad- and medium-band imaging. Identified via strong Ly$\alpha$ lines with extreme Ly$\alpha$ luminosities of ${>}10^{42.6}$ erg s$^{-1}$, the sample exhibits very large rest-frame equivalent widths (${\gtrsim}100$ \AA) and steeply blue UV continua ($\beta_{\rm median}\simeq-2.2$, $-18.2>M_{\rm 1500}>-20.2$ mag). Crucially, the integration of NIRCam medium-band photometry (F410M) breaks the degeneracy between strong rest-optical nebular emission and Balmer breaks, resolving prior mass overestimations. The tightly constrained spectral energy distribution modeling demonstrates that these luminous LAEs tend to be unequivocally low-mass, ultra-young dwarf starbursts; half the sample is characterized by stellar masses of $M_* < 10^8 M_{\odot}$, ages $\lesssim10$ Myr, and negligible dust attenuation. We also map the production efficiency of ionizing photons and Ly$\alpha$ escape fractions ($f_{\rm esc}^{\rm Ly\alpha}$). The $f_{\rm esc}^{\rm Ly\alpha}$ values are exceptionally high, with a median of ${\gtrsim}40$%, increasing for the bluer UV continua. Finally, analyzing spatial offsets between the Ly$\alpha$ centroid and the stellar counterpart, we demonstrate empirically that internal dust content, rather than neutral hydrogen gas, dominate the suppression of Ly$\alpha$ radiative transfer. Our study reveals that strong Ly$\alpha$ emission of the luminous LAEs are generally attributed to both the vigorous starburst activities and the high $f_{\rm esc}^{\rm Ly\alpha}$. Resembling Lyman continuum leakers, these extreme dwarf systems function as highly efficient ionizing engines at the conclusion of the Epoch of Reionization.