MUSE unravels the ionisation and origin of metal enriched absorbers in
  the gas halo of a z = 2.92 radio galaxy
  We have used the Multi-Unit Spectroscopic Explorer (MUSE) to study the
circumgalactic medium (CGM) of a z = 2.92 radio galaxy, MRC 0943-242 by
parametrising its emitting and absorbing gas. In both Ly$\alpha$ $\lambda$1216
and He II $\lambda$1640 lines, we observe emission with velocity shifts of
$\Delta v \simeq-1000$ km s$^{-1}$ from the systemic redshift of the galaxy.
These blueshifted components represent kinematically perturbed gas that is
aligned with the radio axis, which we interpret as jet-driven outflows. Three
of the four known Ly$\alpha$ absorbers are detected at the same velocity as C
IV $\lambda\lambda1548,1551$ and N V $\lambda\lambda1239,1243$ absorbers,
proving that the gas is metal enriched more so than previously thought. At the
velocity of a strong Ly$\alpha$ absorber with an HI column of $N_{\rm HI}/{\rm
cm}^{-2} = 10^{19.2}$ and velocity shift of $\Delta v \simeq -400$ km s$^{-1},$
we also detect Si II $\lambda$1260 and Si II $\lambda$1527 absorption, which
suggests that the absorbing gas is ionisation bounded. With the added
sensitivity of this MUSE observation, we are more capable of adding constraints
to absorber column densities and consequently determining what powers their
ionisation. To do this, we obtain photoionisation grid models in \pkg{cloudy}
which show that AGN radiation is capable of ionising the gas and producing the
observed column densities in a gas of metallicity of Z/Z$_\odot \simeq$ 0.01
with a nitrogen abundance a factor of 10 greater than that of hydrogen. This
metal-enriched absorbing gas, which is also spatially extended over a projected
distance of $r \gtrsim 60$ kpc, is likely to have undergone chemical enrichment
through stellar winds that have swept up metals from the interstellar-medium
and deposited them in the outer regions of the galaxy's halo.
