Presentation #202.01 in the session “Emission Lines in Galaxies: Cosmic Dawn - Let There Be Light (Meeting-in-a-Meeting)”.
When we see Lyman alpha emission from high redshift galaxies, we know that the intergalactic gas around those galaxies must be transmissive — which in turn places upper bounds on the neutral fraction of that medium, because Lyman alpha is resonantly scattered by neutral hydrogen. Variants on this test underlie both some of the earliest evidence for ionized gas at z>6.5, and arguments for a significantly neutral medium at z > 7. In both the LAGER Survey (Lyman Alpha Galaxies in the Epoch of Reionization) at redshift z=7, and the Cosmic DAWN Survey (Deep And Wide Narrowband) at z=7.7, we are seeing Lyman-alpha emitters with large equivalent widths that imply ionized surroundings. We are also seeing evidence for inhomogeneities and ionized bubbles up to redshift z=7.7. I will close by discussing prospects for JWST followup, including planned cycle 1 observations of LAGER survey objects.