摘要：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 (Hα/Hβobs ~ 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.
关键词：ISM: clouds;HII regions;galaxies: active;ISM: jets and outflows;galaxies: individual: Centaurus A
