Ly$\alpha$ Emission from [OIII] Emitters Near Reionization: The role of environment in galaxy Ly$\alpha$ detection

TL;DR

This study investigates how galaxy environment influences Ly$ ext{alpha}$ emission detectability near the end of reionization, using JWST-selected galaxies and Keck observations to explore environmental effects on Ly$ ext{alpha}$ transmission.

Contribution

It provides new observational evidence that environment significantly affects Ly$ ext{alpha}$ emission detection in galaxies at $z \,\sim\ 5$--6, highlighting the role of local structures and neutral islands.

Findings

Ly$ ext{alpha}$ detection fraction varies with environment.

Deficit of Ly$ ext{alpha}$ in a large group near the quasar's ionized zone.

Enhanced Ly$ ext{alpha}$ emission in certain groups suggests environmental influence.

Abstract

Using galaxy Ly$\alpha$ emission to probe reionization relies on establishing baseline expectations for its detectability in the absence of attenuation by neutral gas in the IGM. Towards this end, the growing numbers of $z \sim 5$--6 star-forming galaxies spectroscopically selected by JWST provide an ideal sample for determining how Ly$\alpha$ emission depends on galaxy properties and environment after reionization has largely completed. In this study, we use Keck LRIS to measure the Ly$\alpha$ emission of 46 JWST-selected [OIII]-emitting galaxies over $5.3 \lesssim z \lesssim 6.2$ in the foreground of the ultra-luminous quasar J0100+2802. Overall, we find that the fraction of galaxies detected in Ly$\alpha$ emission is consistent with previous works; however, the fraction also varies with environment. Most notably, we find an apparent deficit of Ly$\alpha$ in the largest group in our sample, at $z \simeq 6.19$, which falls within the redshift range of the quasar's highly ionized proximity zone. We speculate that the Ly$\alpha$ emission from this group may be partly scattered by a foreground neutral island. In contrast, we detect a high rate of Ly$\alpha$ emission in two groups at $z \simeq 5.73$ and $z \simeq 5.78$. These groups may be part of a structure that is extended along the line of sight, enhancing the transmission of Ly$\alpha$ emission. While our sample size is limited, our results suggest that environment may play a significant role in the detectability of galaxy Ly$\alpha$ emission even as late as $z \sim 6$.