Statistics of 207 lyα emitters at a redshift near 7: Constraints on reionization and galaxy formation models

We present the Lyα luminosity function (LF), clustering measurements, and Lyα line profiles based on the largest sample to date of 207 Lyα emitters (LAEs) at z = 6.6 on the 1 deg² sky of Subaru/XMM-Newton Deep Survey field. Our z = 6.6 Lyα LF including cosmic variance estimates yields the best-fit Schechter parameters of φ^* = 8.5^+3.0 _-2.2×10 ^-4 Mpc^-3 and L _Lyα = 4.4 ^+0.6_-0.6 ×10⁴² erg s^-1 with a fixed α = -1.5, and indicates a decrease from z = 5.7 at the≳90% confidence level. However, this decrease is not large, only ≃30% in Lyα luminosity, which is too small to have been identified in the previous studies. A clustering signal of z = 6.6 LAEs is detected for the first time. We obtain the correlation length of r₀ = 2-5 h^-1 ₁₀₀ Mpc and a bias of b = 3-6, and find no significant boost of clustering amplitude by reionization at z = 6.6. The average hosting dark halo mass inferred from clustering is 10¹⁰-10¹¹M⊙, and a duty cycle of LAE population is roughly ∼1%, albeit with large uncertainties. The average of our high-quality Keck/DEIMOS spectra shows an FWHM velocity width of 251 ±16 km s^-1. We find no large evolution of the Lyα line profile from z = 5.7 to 6.6, and no anti-correlation between Lyα luminosity and line width at z = 6.6. The combination of various reionization models and our observational results about the LF, clustering, and line profile indicates that there would exist a small decrease of the intergalactic medium's (IGM's) Lyα transmission owing to reionization, but that the hydrogen IGM is not highly neutral at z = 6.6. Our neutral-hydrogen fraction constraint implies that the major reionization process took place at z ≳ 7.