Abstract

 While the end of reionization is a frequent target of observations, how this process begins, and what causes it are presently unconstrained. One scenario allows reionization to start late and complete rapidly, where moderately luminous galaxies dominate the ionizing photon budget (Robertson et al. 2015). Another scenario allows a smooth temporal evolution of reionization, where very faint galaxies, common at early times, dominate the photon budget (Finkelstein et al. 2019). These models differ drastically in their predictions for the ionized fraction at z~9 (~20% vs. ~60%), and our recent MOSFIRE program has sought Lyα emission at this epoch to distinguish between these two possibilities. We have implemented improved data reduction and stacking of spectra, which accounts for the drift of objects in the slits throughout the night, and unknown offsets of our objects from the expected location in the slit. In this talk, I will show our Lyα detection at z=8.661 in the EGS field in 9.53 hours of integration. This galaxy lies physically close (3.5 pMpc) to another confirmed galaxy in this field, with Lyα detected at z=8.684 (Zitrin et al. 2015).  Our sources might suggest the presence of the highest redshift overdensity in the reionization era, indicate the existence of ≥1Mpc ionized bubbles as early as 500Myr after the Big Bang, and shed light on galaxy growth in the early universe.