  Galactic outflows are believed to play a critical role in the evolution of
galaxies by regulating their mass build-up and star formation. Theoretical
models assumes bipolar shapes for the outflows that extends well into the
circumgalctic medium (CGM), up to tens of kpc perpendicular to the galaxies.
They have been directly observed in the local Universe in several individual
galaxies, e.g., around the Milky Way and M82. At higher redshifts, cosmological
simulations of galaxy formation predict an increase in the frequency and
efficiency of galactic outflows due to the increasing star formation activity.
Outflows are responsible for removing potential fuel for star formation from
the galaxy, while at the same enriching the CGM and the intergalactic medium.
These feedback processes, although incorporated as key elements of cosmological
simulations, are still poorly constrained on CGM scales. Here we present an
ultra-deep MUSE image of the mean MgII emission surrounding a sample of
galaxies at z~1 that strongly suggests the presence of outflowing gas on
physical scales of more than 10kpc. We find a strong dependence of the detected
signal on the inclination of the central galaxy, with edge-on galaxies clearly
showing enhanced MgII emission along the minor axis, while face-on galaxies
display much weaker and more isotropic emission. We interpret these findings as
supporting the idea that outflows typically have a bipolar cone geometry
perpendicular to the galactic disk. We demonstrate that the signal is not
dominated by a few outliers. After dividing the galaxy sample in subsamples by
mass, the bipolar emission is only detected in galaxies with stellar mass
$\mathrm{M_* \gtrsim 10^{9.5} M_\odot}$.
