Probing the AGN Unification Model at redshift z $\sim$ 3 with MUSE
  observations of giant Ly$\alpha$ nebulae
  A prediction of the classic active galactic nuclei (AGN) unification model is
the presence of ionisation cones with different orientations depending on the
AGN type. Confirmations of this model exist for present times, but it is less
clear in the early Universe. Here, we use the morphology of giant Ly$\alpha$
nebulae around AGNs at redshift z$\sim$3 to probe AGN emission and therefore
the validity of the AGN unification model at this redshift. We compare the
spatial morphology of 19 nebulae previously found around type I AGNs with a new
sample of 4 Ly$\alpha$ nebulae detected around type II AGNs. Using two
independent techniques, we find that nebulae around type II AGNs are more
asymmetric than around type I, at least at radial distances $r>30$~physical kpc
(pkpc) from the ionizing source. We conclude that the type I and type II AGNs
in our sample show evidence of different surrounding ionising geometries. This
suggests that the classical AGN unification model is also valid for
high-redshift sources. Finally, we discuss how the lack of asymmetry in the
inner parts (r$\lesssim$30 pkpc) and the associated high values of the HeII to
Ly$\alpha$ ratios in these regions could indicate additional sources of (hard)
ionizing radiation originating within or in proximity of the AGN host galaxies.
This work demonstrates that the morphologies of giant Ly$\alpha$ nebulae can be
used to understand and study the geometry of high redshift AGNs on
circum-nuclear scales and it lays the foundation for future studies using much
larger statistical samples.
