Studying the ISM at $\sim$10 pc scale in NGC 7793 with MUSE -- II.
  Constraints on the oxygen abundance and ionising radiation escape
  We study the ionised ISM in NGC 7793 with MUSE/AO, at a spatial resolution of
$\sim$ 10 pc. The data are complemented with young star clusters (YSCs), O
stars and GMCs observed with HST and ALMA. Using a strong-line method, we find
a median $12 + \log(O/H) \sim 8.37$ with a scatter of 0.25 dex, in agreement
with previous estimates. The abundance map is rich in substructures,
surrounding clusters and massive stars, although clear degeneracies with
photoionisation are present. We determine the observed total amount of ionising
photons, $Q(H^0)$, from the extinction corrected H$\alpha$ luminosity, and
compare it to the expected $Q(H^0)$ obtained by summing the contributions of
YSCs and massive stars, to obtain an escape fraction ($f_{esc}$). Overall, we
find $f_{esc, HII} = 0.67_{-0.12}^{+0.08}$ for the population of HII regions.
We also conclude that the sources of ionisation observed within the FoV are
more than sufficient to explain the amount of diffuse ionised gas observed in
this region of the galaxy. In general, we find that YSCs located in HII regions
have a higher probability to be younger, less massive, and to emit a higher
number of ionising photons than clusters in the rest of the field. Finally, we
study the optical depth of the regions traced by [SII]/[OIII], finding no
systematic trend between the resulting ionisation structure and $f_{esc}$.
[abridged]
