The Spectroscopic Properties of Ly{\alpha}-Emitters at z $\approx$ 2.7:
  Escaping Gas and Photons from Faint Galaxies
  We present a spectroscopic survey of 318 faint $(R\sim 27$, $L\sim0.1L_*)$,
Ly{\alpha}-emission-selected galaxies (LAEs) at 2.5<z<3. A sample of 32 LAEs
with rest-frame optical spectra from Keck/MOSFIRE are used to interpret the LAE
spectra in the context of their systemic redshifts. We find that the Ly{\alpha}
emission of LAEs is typically less spectrally extended than among samples of
more luminous continuum-selected galaxies (LBGs) at similar redshifts. Using
the MOSFIRE subsample, we find that the peak of the Ly{\alpha} line is shifted
by +200 km/s with respect to systemic across a diverse set of galaxies
including both LAEs and LBGs. We also find a small number of objects with
significantly blueshifted Ly{\alpha} emission, a potential indicator of
accreting gas. The Ly{\alpha}-to-H{\alpha} line ratios suggest that the LAEs
have Ly{\alpha} escape fractions $f_{\rm esc,Ly{\alpha}} \approx 30$%,
significantly higher than typical LBG samples. Using redshifts calibrated by
our MOSFIRE sample, we construct composite LAE spectra, finding the first
evidence for metal-enriched outflows in such intrinsically-faint high-redshift
galaxies. These outflows have smaller continuum covering fractions $(f_c
\approx 0.3)$ and velocities $(v_{\rm ave} \approx 100-200$ km/s, $v_{\rm max}
\approx 500$ km/s$)$ than those associated with typical LBGs, suggesting that
gas covering fraction is a likely driver of the high Ly{\alpha} and
Ly-continuum escape fractions of LAEs. Our results suggest a similar scaling of
outflow velocity with star formation rate as is observed at lower redshifts
$(v_{\rm outflow} \sim {\rm SFR}^{0.25})$ and indicate that a substantial
fraction of gas is ejected with $v > v_{esc}$.
