  We use the large spectroscopic data set of the MOSFIRE Deep Evolution Field
survey to investigate the kinematics and energetics of ionised gas outflows.
Using a sample of 598 star-forming galaxies at redshift 1.4 < $z$ < 3.8, we
decompose $\rm{H}\alpha$ and [OIII] emission lines into narrow and broad
components, finding significant detections of broad components in 10% of the
sample. The ionised outflow velocity from individual galaxies appears
independent of galaxy properties, such as stellar mass, star-formation rate
(SFR), and star-formation-rate surface density ($\Sigma_{\rm SFR}$). Adopting a
simple outflow model, we estimate the mass-, energy- and momentum-loading
factors of the ionised outflows, finding modest values with averages of 0.33,
0.04, and 0.22, respectively. The larger momentum- than energy-loading factors,
for the adopted physical parameters, imply that these ionised outflows are
primarily momentum-driven. We further find a marginal correlation (2.5$\sigma$)
between the mass-loading factor and stellar mass in agreement with predictions
by simulations, scaling as $\eta_{m}$ $\propto M_{\star}^{-0.45}$. This shallow
scaling relation is consistent with these ionised outflows being driven by a
combination of mechanical energy generated by supernovae explosions and
radiation pressure acting on dusty material. In a majority of galaxies, the
outflowing material does not appear to have sufficient velocity to escape the
gravitational potential of their host, likely recycling back at later times.
Together, these results suggest that the ionised outflows traced by nebular
emission lines are negligible, with the bulk of mass and energy carried out in
other gaseous phases.
