WHAT IS THE PHYSICAL ORIGIN OF STRONG Ly alpha EMISSION? II. GAS KINEMATICS AND DISTRIBUTION OF Ly alpha EMITTERS

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 similar or equal to 2. We make a sample of 22 LAEs with a large Ly alpha equivalent width (EW) of greater than or similar to 50 angstrom 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 Ly alpha from a systemic redshift determined with nebular lines to be Delta upsilon(Ly alpha) = 234 +/- 9 km s(-1). Using a Kolmogorov-Smirnov test, we confirm the previous claim of Hashimoto et al. that the average Delta upsilon(Ly alpha) 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 Delta upsilon(IS) = 204 +/- 27 km s(-1), indicating LAEs' gas outflow with a velocity comparable to typical LBGs. Thus, the ratio R-IS(Ly alpha) = Delta upsilon(Ly alpha)/Delta upsilon(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.