Embedded star formation in the extended narrow line region of Centaurus
  A: extreme mixing observed by MUSE
  We present a detailed study of the complex ionization structure in a small
(~250 pc) extended narrow line region (ENLR) cloud near Centaurus A using the
Multi Unit Spectroscopic Explorer. This cloud is located in the so-called outer
filament of ionized gas (about 15 kpc from the nucleus) where jet-induced star
formation has been suggested to occur by different studies. We find that,
despite the small size, a mixture of ionization mechanisms is operating,
resulting in considerable complexity in the spatial ionization structure. The
area includes two H II regions where star formation is occurring and another
location where star formation must have ceased very recently. Interestingly,
the extreme Balmer decrement of one of the star forming regions
(H_alpha/H_beta~6) indicates that it is still heavily embedded in its natal
cocoon of gas and dust. At all three locations a continuum counterpart is found
with spectra matching those of O/B stars local to Centaurus A. The H II regions
are embedded in a larger gas complex which is photoionized by the radiation of
the central active galactic nucleus (AGN), but the O/B stars affect the spatial
ionization pattern in the ENLR cloud very locally. In particular, in the
surroundings of the youngest star forming region, we can isolate a tight mixing
sequence in the diagnostic diagram going from gas with ionization due to a pure
stellar continuum to gas only photoionized by the AGN. These results emphasize
the complexity and the mixture of processes occurring in star forming regions
under the influence of an AGN radiation. This is relevant for our understanding
of AGN-induced star formation suggested to occur in a number of objects,
including this region of Centaurus A. They also illustrate that these young
stars influence the gas over only a limited region.
