The Web Epoch of Reionization Lyman-$\hat{I}\pm$ Survey (WERLS) I. MOSFIRE Spectroscopy of $\mathbf{z}\sim 7-8$ Lyman-$\hat{I}\pm$ Emitters

Abstract

We present the first results from the Web Epoch of Reionization Lyman-$\hat{I}\pm$ Survey (WERLS), a spectroscopic survey of Lyman-$\hat{I}\pm$ emission using Keck I/MOSFIRE and LRIS. WERLS targets bright ($J<26$) galaxy candidates with photometric redshifts of $5.5\lesssim z\lesssim 8$ selected from pre-JWST imaging embedded in the Epoch of Reionization (EoR) within three JWST deep fields: CEERS, PRIMER, and COSMOS-Web. Here, we report 11 $z\sim 7-8$ Lyman-$\hat{I}\pm$ emitters (LAEs; 3 secure and 8 tentative candidates) detected in the first five nights of WERLS MOSFIRE data. We estimate our observed LAE yield is $\sim 13$%, broadly consistent with expectations assuming some loss from redshift uncertainty, contamination from sky OH lines, and that the Universe is approximately half-ionized at this epoch, whereby observable Lyman-$\hat{I}\pm$ emission is unlikely for galaxies embedded in a neutral intergalactic medium. Our targets are selected to be UV-bright, and span a range of absolute UV magnitudes with $-23.1<M_{\text{UV}}<-19.8$. With two LAEs detected at $z=7.68$, we also consider the possibility of an ionized bubble at this redshift. Future synergistic Keck+JWST efforts will provide a powerful tool for pinpointing beacons of reionization and mapping the large scale distribution of mass relative to the ionization state of the Universe.

27 pages, 8 figures; ApJ submitted