Gas Motion Study of Lya Emitters at z~2 Using UV and Optical Spectral
  Lines
  We present the results of Magellan/MMIRS and Keck/NIRSPEC spectroscopy for
five Lya emitters (LAEs) at z=2.2 for which high-resolution FUV spectra from
Magellan/MagE are available. We detect nebular emission lines including Ha on
the individual basis and low-ionization interstellar (LIS) absorption lines in
a stacked FUV spectrum, and measure average offset velocities of the Lya line,
Delta_v_Lya, and LIS absorption lines, Delta_v_abs, with respect to the
systemic velocity defined by the nebular lines. For a sample of eight z~2-3
LAEs without AGN from our study and the literature, we obtain Delta_v_Lya =
175+/-35 km s^{-1}, which is significantly smaller than that of Lyman-break
Galaxies (LBGs), Delta_v_Lya=400 km s^{-1}. The stacked FUV spectrum gives
Delta_v_abs = -179 +/- 73 km s^{-1}, comparable to that of LBGs. These positive
Delta_v_Lya and negative Delta_v_abs suggest that LAEs also have outflows. In
contrast to LBGs, however, the LAEs' Delta_v_Lya is as small as |Delta_v_abs|,
suggesting low neutral hydrogen column densities. Such a low column density
with a small number of resonant scattering may cause the observed strong Lya
emission of LAEs. We find an anti-correlation between Lya equivalent width (EW)
and Delta_v_Lya 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
Delta_v_Lya values, constraints on the reionization history derived from the
Lya transmissivity may need to be revised.
