detections or non-detections, is valuable toward building up a statistical sample that is large enough to constrain the reionization process as well as studying in detail the physical properties of galaxies via further follow-up observations, and is thus being actively pursued.

This paper extends such previous and on-going attempts. In this study, we report Ly$\alpha$ emission from a galaxy at $z=7.66$ in the Great Observatories Origins Deep Survey South [GOODS-S; @giavalisco04] field. This is from a very deep spectroscopic follow-up campaign of $z \sim$ 7–8 galaxy candidates with the Multi-Object Spectrometer For Infra-Red Exploration [MOSFIRE; @mclean12] on the Keck I 10 m telescope, where we push the median 5$\sigma$ limiting sensitivity in line flux down to $\sim 5 \times 10^{-18}$ erg s$^{-1}$ cm$^{-2}$ between sky lines. Although limited by the small number of observed galaxies, we discuss the implications of our results in the context of the evolution of the Ly$\alpha$ visibility.

This paper is organized as follows. Section \[sec:data\] describes our target selection, deep spectroscopic observations with MOSFIRE, and data reduction. Section \[sec:results\] and \[sec:sedfit\] present the results from our spectroscopy and our stellar population modeling, respectively. The implication of our observations on the Ly$\alpha$ visibility is presented in 