IFU spectroscopy of 10 early-type galactic nuclei - III. Properties of
  the circumnuclear gas emission
  Many Early-type galaxies (ETG) have ionized gas emission in their centres
that extends to scales of ~ 1kpc. The majority of such objects are classified
as LINERs, but the nature of their ionizing source is still not clear. The
kinematics associated with these gaseous structures usually shows deviations
from a pure rotational motion due to non-gravitational effects or to
non-axisymmetric potentials. This is the third of a series of papers that
describes a sample of 10 nearby and massive ETG observed with the Gemini
Multi-Object Spectrograph in Integral Field mode installed on the Gemini-South
telescope. In paper II, we performed spectral synthesis to subtract the stellar
components from the data cubes of the sample galaxies in order to study their
nuclear spectra. Here, we analyse the circumnuclear gas emission (scales of ~
100 pc) of the sample galaxies. Circumnuclear gas emission was detected in
seven galaxies, all of them classified as LINERs. Pure gaseous discs are found
in three galaxies. In two objects, gaseous discs are probably present, but
their kinematics are affected by non-Keplerian motions. In IC 5181, we detected
a spiral structure of gas that may be caused either by a non-axisymmetric
potential or by an outflow together with a gaseous disc. In NGC 3136, an
ionization bicone is present in addition to five compact structures with
LINER-like emission. In galaxies with a gaseous disc, we found that ionizing
photons emitted by an AGN are not enough to explain the observed Ha flux along
this structure. On the other hand, the Ha flux distribution and equivalent
width along the direction perpendicular the gaseous disc suggest the presence
of low-velocity ionized gas emission which seem to be related to the nuclear
activity. We propose a scenario for LINER-like circumnuclear regions where a
low-velocity ionization cone is formed by a collimating agent aligned with the
gaseous disc.
