The clustering of Lyman α emitters at z ≈ 7: Implications for reionization and host halo masses

The Lyman α (Lyα) line of high-redshift galaxies has emerged as a powerful probe of both early galaxy evolution and the epoch of reionization (EoR). Motivated by the upcoming wide-field survey with the Subaru Hyper Suprime-Cam (HSC), we study the angular correlation function (ACF) of narrow-band selected, z ≈ 7 Lyα emitting galaxies (LAEs). The clustering of LAEs is determined by both (i) their typical host halo masses, M_h, and (ii) the absorption due to a patchy EoR, characterized by an average neutral fraction of the intergalactic medium, x_HI. We bracket the allowed LAE ACFs by exploring extreme scenarios for both the intrinsic Lya emission and the large-scale pattern (i.e. morphology) of cosmic ionized patches in physical EoR models. Independent of the EoR morphology, current z ≈ 7 ACF measurements constrain x _HI ≲ 0.5 (1σ). We also find that the low values of the currently observed ACF imply that LAEs are hosted by relatively small dark matter haloes: M_h ≲ 10¹⁰M_⊙, with corresponding duty cycles of ≲few per cent. These values are over an order of magnitude lower than the analogous ones for colour-selected, Lyman break galaxies, suggesting that z ≈ 7 narrowband LAEs searches are preferentially selecting young, starburst galaxies, residing in less massive haloes. The upcoming Ultra Deep campaign with the HSC will significantly improve constraints on both the EoR and LAE host haloes.