We investigate Ly \alpha , [ Oiii ] \lambda 5007 , H \alpha , and [ Cii ] 158 \mu m emission from 1 , 124 galaxies at z = 4.9 - 7.0 .
Our sample is composed of 1 , 092 Ly \mathrm { \alpha } 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 Subaru/HSC ( SPLASH ) and 34 galaxies at z = 5.148 - 7.508 with deep ALMA [ Cii ] 158 \mu m data in the literature .
Fluxes of strong rest-frame optical lines of [ Oiii ] and H \mathrm { \alpha } ( H \beta ) are constrained by significant excesses found in the SPLASH 3.6 and 4.5 \mathrm { \mu m } photometry .
At z = 4.9 , we find that the rest-frame H \alpha equivalent width and the Ly \alpha escape fraction f _ { Ly \alpha } positively correlate with the rest-frame Ly \alpha equivalent width EW ^ { 0 } _ { \mathrm { Ly \alpha } } .
The f _ { Ly \alpha } - EW ^ { 0 } _ { \mathrm { Ly \alpha } } correlation is similarly found at z \sim 0 - 2 , suggesting no evolution of the correlation over z \simeq 0 - 5 .
The typical ionizing photon production efficiency of LAEs is \mathrm { log } \xi _ { \mathrm { ion } } / \mathrm { [ Hz erg ^ { -1 } ] } \simeq 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 turn-over trend that the [ Oiii ] / \mathrm { H \alpha } flux ratio increases in EW ^ { 0 } _ { \mathrm { Ly \alpha } } \simeq 0 - 30 \mathrm { \AA } , and then decreases out to EW ^ { 0 } _ { \mathrm { Ly \alpha } } \simeq 130 \mathrm { \AA } .
We also identify an anti-correlation between a [ Cii ] luminosity to star-formation rate ratio ( L _ { \mathrm { [ CII ] } } / SFR ) and EW ^ { 0 } _ { \mathrm { Ly \alpha } } at the > 99 \% confidence level .
We carefully investigate physical origins of the correlations with stellar-synthesis and photoionization models , and find that a simple anti-correlation between EW _ { \mathrm { Ly \alpha } } ^ { 0 } and metallicity explains self-consistently all of the correlations of Ly \alpha , H \alpha , [ Oiii ] / \mathrm { H \alpha } , and [ Cii ] identified in our study , indicating detections of metal-poor ( \sim 0.03 Z _ { \odot } ) galaxies with EW ^ { 0 } _ { \mathrm { Ly \alpha } } \simeq 200 \mathrm { \AA } .