What is the physical origin of strong Lyα emission? II. Gas kinematics and distribution of Lyα emitters

We present a statistical study of velocities of Lyα, interstellar (IS) absorption, and nebular lines and gas covering fraction for Lyα emitters (LAEs) at z ≅ 2. We make a sample of 22 LAEs with a large Lyα equivalent width (EW) of ≳ 50 Å based on our deep Keck/Low Resolution Imaging Spectrometer (LRIS) observations, in conjunction with spectroscopic data from the Subaru/Fiber Multi Object Spectrograph program and the literature. We estimate the average velocity offset of Lyα from a systemic redshift determined with nebular lines to be Δv _Lyα = 234 ± 9 km s^–1. Using a Kolmogorov-Smirnov test, we confirm the previous claim of Hashimoto et al. that the average Δv _Lyα of LAEs is smaller than that of Lyman break galaxies (LBGs). Our LRIS data successfully identify blueshifted 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 Δv _IS = 204 ± 27 km s^–1, indicating LAEs' gas outflow with a velocity comparable to typical LBGs. Thus, the ratio R_IS^Lyα≡Δv_Lyα/Δv_IS of LAEs is around unity, suggestive of low impacts on Lyα transmission by resonant scattering of neutral hydrogen in the IS medium. We find an anti-correlation between Lyα 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 _{H I}. The results of our study support the idea that N _{H I} is a key quantity determining Lyα emissivity.