Near-ultraviolet Spectroscopy of Star-forming Galaxies from eBOSS:
  Signatures of Ubiquitous Galactic-scale Outflows
  We present the rest-frame near-ultraviolet (NUV) spectroscopy of star-forming
galaxies (SFGs) at 0.6<z<1.2 from the Extended Baryon Oscillation Spectroscopic
Survey (eBOSS) in SDSS-IV. One of the eBOSS programs is to obtain 2 arcsec
(about 15 kpc) fiber spectra of about 200,000 emission-line galaxies (ELGs) at
redshift z>0.6. We use the data from the pilot observations of this program,
including 8620 spectra of SFGs at 0.6<z<1.2. The median composite spectra of
these SFGs at 2200 Ang < \lambda < 4000 Ang feature asymmetric, preferentially
blueshifted non-resonant emission, Fe II*, and blueshifted resonant absorption,
e.g., Fe II and Mg II, indicating ubiquitous outflows driven by star formation
at these redshifts. For the absorption lines, we find a variety of velocity
profiles with different degrees of blueshift. Comparing our new observations
with the literature, we do not observe the non-resonant emission in the
small-aperture (<40 pc) spectra of local star-forming regions with the Hubble
Space Telescope, and find the observed line ratios in the SFG spectra to be
different from those in the spectra of local star-forming regions, as well as
those of quasar absorption-line systems in the same redshift range. We
introduce an outflow model that can simultaneously explain the multiple
observed properties and suggest that the variety of absorption velocity
profiles and the line ratio differences are caused by scattered fluorescent
emission filling in on top of the absorption in the large-aperture eBOSS
spectra. We develop an observation-driven, model-independent method to correct
the emission-infill to reveal the true absorption profiles. Our results show
that eBOSS and future dark-energy surveys (e.g., DESI and PFS) will provide
rich datasets of NUV spectroscopy for astrophysical applications.
