Stacked Rest-Frame UV Spectra of Ly$\alpha$-Emitting and
  Continuum-Selected Galaxies at 2<z<3.5
  We present properties of individual and composite rest-UV spectra of
continuum- and narrowband-selected star-forming galaxies (SFGs) at a redshift
of 2<z<3.5 discovered by the MUSYC collaboration in the ECDF-S. Among our
sample of 81 UV-bright SFGs, 59 have R<25.5, of which 32 have rest-frame
equivalent widths W_{Ly{\alpha}}>20 {\AA}, the canonical limit to be classified
as a LAE. We divide our dataset into subsamples based on properties we are able
to measure for each individual galaxy: Ly{\alpha} equivalent width, rest-frame
UV colors, and redshift. Among our subsample of galaxies with R<25.5, those
with rest-frame W_{Ly{\alpha}}>20 {\AA} have bluer UV continua, weaker
low-ionization interstellar absorption lines, weaker C IV absorption, and
stronger Si II* nebular emission than those with W_{Ly{\alpha}}<20 {\AA}. We
measure a typical velocity offset of {\Delta}v~600 km s$^{-1}$ between
Ly{\alpha} emission and low-ionization absorption among our subsamples. We find
that the interstellar component, as opposed to the stellar component, dominates
the high-ionization absorption line profiles. We find the low- and
high-ionization Si ionization states have similar kinematic properties, yet the
low-ionization absorption is correlated with Ly$\alpha$ emission and the
high-ionization absorption is not. These trends are consistent with outflowing
neutral gas being in the form of neutral clouds embedded in ionized gas as
previously suggested by \cite{Steidel2010}. Moreover, our galaxies with bluer
UV colors have stronger Ly{\alpha} emission, weaker low-ionization absorption
and more prominent nebular emission line profiles. Among our dataset, UV-bright
galaxies with W_{Ly{\alpha}}>20 {\AA} exhibit weaker Ly{\alpha} emission at
lower redshifts, although we caution that this could be caused by spectroscopic
confirmation of low Ly{\alpha} equivalent width galaxies being harder at z~3
than z~2.
