We present a statistical study of velocities of Ly \alpha , interstellar ( IS ) absorption , and nebular lines and gas covering fraction for Ly \alpha emitters ( LAEs ) at z \simeq 2 .
We make a sample of 22 LAEs with a large Ly \alpha equivalent width ( EW ) of \gtrsim 50 Å based on our deep Keck/LRIS observations , in conjunction with spectroscopic data from the Subaru/FMOS program and the literature .
We estimate the average velocity offset of Ly \alpha from a systemic redshift determined with nebular lines to be \Delta v _ { Ly \alpha } = 234 \pm 9 km s ^ { -1 } .
Using a Kolmogorv-Smirnov test , we confirm the previous claim of Hashimoto et al .
( 2013 ) that the average \Delta v _ { Ly \alpha } of LAEs is smaller than that of LBGs .
Our LRIS data successfully identify blue-shifted multiple IS absorption lines in the UV continua of four LAEs on an individual basis .
The average velocity offset of IS absorption lines from a systemic redshift is \Delta v _ { IS } = 204 \pm 27 km s ^ { -1 } , indicating LAE ’ s gas outflow with a velocity comparable to typical LBGs .
Thus , the ratio , R ^ { Ly \alpha } _ { IS } \equiv \Delta v _ { Ly \alpha } / \Delta v _ { IS } of LAEs , is around unity , suggestive of low impacts on Ly \alpha transmission by resonant scattering of neutral hydrogen in the IS medium .
We find an anti-correlation between Ly \alpha EW and the covering fraction , f _ { c } , estimated from the depth of absorption lines , where f _ { c } is an indicator of average neutral hydrogen column density , N _ { HI } .
The results of our study support the idea that N _ { HI } is a key quantity determining Ly \alpha emissivity .