2016MNRAS.463.1678S

We present new results from the widest narrow band survey search for Lyα emitters at z = 5.7, just after reionization. We survey a total of 7 deg² spread over the COSMOS, UDS and SA22 fields. We find over 11,000 line emitters, out of which 514 are robust Ly_α candidates at z = 5.7 within a volume of 6.3 x 10⁶ Mpc3. Our Ly_α emitters span a wide range in Ly_α luminosities, from faint to bright (LLy_α ∼ 10^42.5 - 44^ erg/s) and rest-frame equivalent widths (EW0 ∼ 25 - 1000 Å) in a single, homogeneous data-set. By combining all our fields we find that the faint end slope of the z = 5.7 Ly_α luminosity function is very steep, with α =-2.3^+0.4_–0.3. We also present an updated z = 6.6 Ly_α luminosity function, based on comparable volumes and obtained with the same methods, which we directly compare with that at z = 5.7. We find a significant decline of the number density of faint Ly_α emitters from z = 5.7 to z = 6.6 (by 0.5 ± 0.1 dex), but no evolution at the bright end/no evolution in L^*. Faint Lyα emitters at z = 6.6 show much more extended haloes than those at z = 5.7, suggesting that neutral Hydrogen plays an important role, increasing the scattering and leading to observations missing faint Lyα emission within the epoch of reionization. All together, our results suggest that we are observing patchy reionization which happens first around the brightest Lyα emitters, allowing the number densities of those sources to remain unaffected by the increase of neutral Hydrogen fraction from z ∼ 5 to z ∼ 7.