Lyman-$\alpha$ Visibility During the Epoch of Reionization: Combining JWST FRESCO Grism Data with Keck Archival Spectroscopy

TL;DR

This study combines JWST FRESCO and Keck archival data to analyze the environments and properties of Lyman-$\alpha$ emitters at $z>7$, revealing that overdensity alone does not explain Lyman-$\alpha$ visibility during reionization.

Contribution

It introduces a new sample of 14 high-redshift LAEs with combined JWST and Keck data, and assesses their environments and properties to understand Lyman-$\alpha$ visibility during reionization.

Findings

Bright LAEs are not in more overdense regions than average galaxies.

LAEs have slightly higher recent star formation rates and [OIII] equivalent widths.

Overdensity alone does not fully account for Lyman-$\alpha$ visibility.

Abstract

The visibility of Lyman-$\alpha$ emission at $z>7$ provides crucial insights into the reionization process and the role of galaxies in shaping the ionized intergalactic medium. Using JWST FRESCO data, we investigate the environments of Lyman-$\alpha$ emitters (LAEs) in the GOODS-N and GOODS-S fields by identifying [OIII] emitters and analyzing their large-scale distribution. Using the FRESCO redshifts, we recover eight new LAEs from archival Keck/MOSFIRE observations at $z=7.0-7.7$, including a potential AGN candidate at $z \sim 7.2$. Complemented by six literature LAEs, our sample consists of 14 LAEs in total, all of which are [OIII] emitters except for one very faint source not detected by FRESCO. We define seven groups of [OIII] emitters centered around the brightest LAEs and find that these bright LAEs do not reside in more overdense environments than the average galaxy population. The overdensity parameters for LAEs and [OIII] emitters without Lyman-$\alpha$, calculated for sources with $\mathrm{M_{UV}<-19.5}$ to ensure completeness, are similar, indicating that overdensities alone cannot fully explain Lyman-$\alpha$ visibility. While LAEs have slightly higher recent star formation (SFR$_{10}$/SFR$_{50} \approx 1.3\times$) and [OIII] EW ($\approx1.5\times$), they show no significant differences from [OIII] emitters in UV slope ($\beta$), UV magnitude ($\mathrm{M_{UV}}$), or stellar mass ($\log_{\mathrm{M}_{\star}}$). Our results suggest that other factors may contribute to the observability of Lyman-$\alpha$ emission. Future spectroscopic surveys with broader wavelength coverage and more complete sampling will be crucial for refining our understanding of reionization.