  We study in detail the inner 600 pc of the Seyfert 2 galaxy ESO138-G001 by
means of the SOAR Integral Field Spectrograph (SIFS) attached to the SOAR
telescope. This source is known for displaying a very rich coronal line
spectrum and a blob of high-excitation emission ~3" SE of the active galactic
nucleus (AGN). The nature of this emission has not been fully understood yet.
The excellent spatial and spectral resolution of SIFS allows us to confirm that
the bulk of the coronal line forest emission region is very compact, of ~0.8"
in diameter, centred on the AGN and most likely powered by radiation from the
AGN. In addition, evidence of a nuclear outflow, restricted to the inner 1"
centred at the nucleus is found based on the detection of broad components in
the most important emission lines. The gas in the inner few tens of parsecs
filters out the AGN continuum so that the NLR is basically illuminated by a
modified SED. This scenario is confirmed by means of photoionisation models
that reproduce the most important lines detected in the SIFS field-of-view.
From the modelling, we also found that the black hole mass M_BH of the AGN is
about 10^5.5 solar mass, in agreement with previous X-ray observations. The
spectrum of the SE blob is dominated by emission lines of low- to
mid-ionisation, with no hints of coronal lines. Our results show that it
represents gas in the ionisation cone that is photoionised by the filtered
central AGN continuum.
