The MOSDEF Survey: Broad Emission Lines at z=1.4-3.8
  We present results from the MOSFIRE Deep Evolution Field (MOSDEF) survey on
broad flux from the nebular emission lines H$\alpha$, [NII], [OIII], H$\beta$,
and [SII]. The sample consists of 127 star-forming galaxies at $1.37 < z <
2.61$ and 84 galaxies at $2.95 < z < 3.80$. We decompose the emission lines
using narrow ($\text{FWHM} < 275 \ \text{km s}^{-1}$) and broad ($\text{FWHM} >
300 \ \text{km s}^{-1}$) Gaussian components for individual galaxies and
stacks. Broad emission is detected at $>3\sigma$ in $<10$% of galaxies and the
broad flux accounts for 10-70% of the total flux. We find a slight increase in
broad to narrow flux ratio with mass but note that we cannot reliably detect
broad emission with $\text{FWHM} < 275 \ \text{km s}^{-1}$, which may be
significant at low masses. Notably, there is a correlation between higher
signal-to-noise (S/N) spectra and a broad component detection indicating a S/N
dependence in our ability to detect broad flux. When placed on the N2-BPT
diagram ([OIII]/H$\beta$ vs. [NII]/H$\alpha$) the broad components of the
stacks are shifted towards higher [OIII]/H$\beta$ and [NII]/$\alpha$ ratios
compared to the narrow component. We compare the location of the broad
components to shock models and find that the broad component could be due to
shocks, but we do not rule out other possibilities such as the presence of an
AGN. We estimate the mass loading factor (mass outflow rate/star formation
rate) assuming the broad component is a photoionized outflow and find that the
mass loading factor increases as a function of mass which agrees with previous
studies. We show that adding emission from shocked gas to $z\sim0$ SDSS spectra
shifts galaxies towards the location of $z\sim2$ galaxies on several emission
line diagnostic diagrams.
