The largest LYα narrow band survey AT Z=5.7: implications for reionization

Tese de mestrado, Física (Astrofísica e Cosmologia) Universidade de Lisboa, Faculdade de Ciências, 2016We 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 Lyα candidates at z = 5:7 within a volume of 6:3 x 106 Mpc3. Our Lyα emitters span a wide range in Lyα luminosities, from faint to bright (LLyα ~ 1042:5-44 erg s-1) and rest-frame equivalent widths (EW0 ~ 25 – 100Ẵ) in a single, homogeneous data-set. By combining all our fields we find that the faint end slope of the z = 5:7 Lyα luminosity function is very steep, with α = -2:3+0:4-0:3. We also present an updated z = 6:6 Lyα 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 Lyα 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 indicate 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