2013ApJ...765...70H

We present the results of Magellan/MMIRS and Keck/NIRSPEC spectroscopy for five Lyα emitters (LAEs) at z ≃ 2.2 for which high-resolution FUV spectra from Magellan/MagE are available. We detect nebular emission lines including Hα on the individual basis and low-ionization interstellar (LIS) absorption lines in a stacked FUV spectrum, and measure average offset velocities of the Lyα line, Δv_Lyα, and LIS absorption lines, Δv_abs, with respect to the systemic velocity defined by the nebular lines. For a sample of eight z ∼ 2-3 LAEs without active galactic nucleus from our study and the literature, we obtain Δv_Lyα = 175±35 km/s, which is significantly smaller than that of Lyman-break Galaxies (LBGs), Δv_Lyα≃ 400 km/s. The stacked FUV spectrum gives Δv_abs= -179±73 km/s, comparable to that of LBGs. These positive Δv_Lyα and negative Δv_abssuggest that LAEs also have outflows. In contrast to LBGs, however, the LAEs' Δv_Lyα is as small as|Δv_abs|, suggesting low neutral hydrogen column densities. Such a low column density with a small number of resonant scattering may cause the observed strong Lyα emission of LAEs. We find an anti-correlation between Lyα equivalent width (EW) and Δv_Lyα in a compilation of LAE and LBG samples. Although its physical origin is not clear, this anti-correlation result appears to challenge the hypothesis that a strong outflow, by means of a reduced number of resonant scattering, produces a large EW. If LAEs at z > 6 have similarly small Δv_Lyαvalues, constraints on the reionization history derived from the Lyα transmissivity may need to be revised.