We present the first results from the ongoing LAGER project (Lyman Alpha Galaxies in the Epoch of Reionization), which is the largest narrowband survey for z ∼ 7 galaxies to date. Using a specially built narrowband filter NB964 for the superb large-area Dark-Energy Camera (DECam) on the NOAO/CTIO 4m Blanco telescope, LAGER has collected 34 hours NB964 narrowband imaging data in the 3 deg 2 COSMOS field. We have identified 23 Lyman Alpha Emitter (LAE) candidates at z = 6.9 in the central 2-deg 2 region, where DECam and public COSMOS multi-band images exist. The resulting luminosity function can be described as a Schechter function modified by a significant excess at the bright end (4 galaxies with L Lyα ∼ 10 43.4±0.2 erg s −1 ). The number density at L Lyα ∼ 10 43.4±0.2 erg s −1 is little changed from z = 6.6, while at fainter L Lyα it is substantially reduced. Overall, we see a fourfold reduction in Lyα luminosity density from z = 5.7 to 6.9. Combined with a more modest evolution of the continuum UV luminosity density, this suggests a factor of ∼ 3 suppression of Lyα by radiative transfer through the z ∼ 7 intergalactic medium (IGM). It indicates an IGM neutral fraction x HI ∼ 0.4-0.6 (assuming Lyα velocity offsets of 100-200 km s −1 ). The changing shape of the Lyα luminosity function between z 6.6 and z = 6.9 supports the hypothesis of ionized bubbles in a patchy reionization at z ∼ 7.

Enormous Lyα Nebulae (ELANe), unique tracers of galaxy density peaks, are predicted to lie at the nodes and intersections of cosmic filamentary structures. Previous successful searches for ELANe have focused on wide-field narrowband surveys, or have targeted known sources such as ultraluminous quasi-stellar-objects (QSOs) or radio galaxies. Utilizing groups of coherently strong Lyα absorptions (CoSLAs), we have developed a new method to identify high-redshift galaxy overdensities and have identified an extremely massive overdensity, BOSS1441, at z = 2 − 3 (Cai et al. 2016a). In its density peak, we discover an ELAN that is associated with a relatively faint continuum. To date, this object has the highest diffuse Lyα nebular luminosity of L nebula = 5.1 ± 0.1 × 10 44 erg s −1 . Above the 2σ surface brightness limit of SB Lyα = 4.8 × 10 −18 erg s −1 cm −2 arcsec −2 , this nebula has an end-to-end spatial extent of 442 kpc. This radio-quiet source also has extended C iv λ1549 and He ii λ1640 emission on 30 kpc scales. Note that the Lyα, He ii and C iv emission all have double-peaked line profiles. Each velocity component has a full-width-half-maximum (FWHM) of ≈ 700 − 1000 km s −1 . We argue that this Lyα nebula could be powered by shocks due to an AGN-driven outflow or/and photoionization by a strongly obscured source.

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