IFU spectroscopy of 10 early-type galactic nuclei - III. Properties of the circumnuclear gas emission

Many early-type galaxies have ionized gas emission in their centres that extends to scales of similar to 1 kpc. The majority of such objects are classified as low-ionization nuclear emission regions (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 (e.g. outflows) or to non-axisymmetric potentials (e.g. bars or tri-axial systems). This is the third of a series of papers that describes a sample of 10 nearby (d < 30 Mpc) and massive (sigma > 200 km s(-1)) early-type galaxies 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. In this work, we analyse the circumnuclear gas emission (scales of similar to 100 pc) of the sample galaxies and we compare the results with those obtained with Principal Component Analysis Tomography in Paper I. We detected circumnuclear gas emission in seven galaxies of the sample, 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 one galaxy (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 active galactic nucleus are not enough to explain the observed H alpha flux along this structure. On the other hand, the H alpha 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. (AU)