  Galactic outflows are critical to our understanding of galaxy formation and
evolution. However the details of the underlying feedback process remain
unclear. We compare Ly$\alpha$ observations of the circumgalactic medium (CGM)
of Lyman Break Galaxies (LBGs) with mock observations of their simulated CGM.
We use cosmological hydrodynamical `zoom-in' simulations of an LBG which
contains strong, momentum-driven galactic outflows. Simulation snapshots at
$z=2.2$ and $z=2.65$ are used, corresponding to the available observational
data. The simulation is post-processed with the radiative transfer code
\textsc{crash} to account for the impact of ionising photons on hydrogen gas
surrounding the simulated LBG. We generate mock absorption line maps for
comparison with data derived from observed close galaxy-galaxy pairs. We
perform calculations of Ly$\alpha$ photons scattering through the CGM with our
newly developed Monte-Carlo code \textsc{slaf}, and compare to observations of
diffuse Ly$\alpha$ halos around LBGs. Our fiducial galactic outflow model comes
closer to reproducing currently observed characteristics of the CGM in
Ly$\alpha$ than a reference inefficient feedback model used for comparison.
Nevertheless, our fiducial model still struggles to reproduce the observed data
of the inner CGM (at impact parameter $b<30$kpc). Our results suggest that
galactic outflows affect Ly$\alpha$ absorption and emission around galaxies
mostly at impact parameters $b<50$ kpc, while cold accretion flows dominate at
larger distances. We discuss the implications of this result, and underline the
potential constraining power of CGM observations - in emission and absorption -
on galactic outflow models.
