2018ApJ...859...84H

We investigate Lyα, [O III] λ5007, Hα, and [C II] 158 µm emission from 1124 galaxies at z = 4.9-7.0. Our sample is composed of 1092 Lyα emitters (LAEs) at z = 4.9, 5.7, 6.6, and 7.0 identified by Subaru/Hyper-Suprime-Cam (HSC) narrowband surveys covered by Spitzer Large Area Survey with Hyper-Suprime-Cam (SPLASH) and 34 galaxies at z = 5.148-7.508 with deep ALMA [C II] 158 µm data in the literature. Fluxes of strong rest-frame optical lines of [O III] and Hα (Hβ) are constrained by significant excesses found in the SPLASH 3.6 and 4.5 µm photometry. At z = 4.9, we find that the rest-frame Hα equivalent width and the Lyα escape fraction f_Lyα positively correlate with the rest-frame Lyα equivalent width EW_Lyα⁰. The f_Lyα–EW_Lyα⁰ correlation is similarly found at z ∼ 0-2, suggesting no evolution of the correlation over z ≃ 0-5. The typical ionizing photon production efficiency of LAEs is log(ξ_ion/[Hz erg^–1]) ≃ 25.5, significantly (60%-100%) higher than those of LBGs at a given UV magnitude. At z = 5.7-7.0, there exists an interesting turnover trend that the [O III]/Hα flux ratio increases in EW_Lyα⁰≃0–30Åand then decreases out to EW_Lyα⁰≃130Å. We also identify an anticorrelation between a ratio of [C II] luminosity to star formation rate (L_[C II]_/SFR) and EW_Lyα⁰ at the >99% confidence level.. We carefully investigate physical origins of the correlations with stellar-synthesis and photoionization models and find that a simple anticorrelation between EW_Lyα⁰ and metallicity explains self-consistently all of the correlations of Lyα, Hα, [O III]/Hα, and [C II] identified in our study, indicating detections of metal-poor (∼0.03 Z_☉) galaxies with EW_Lyα⁰≃200Å.