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

TL;DR

This study investigates the properties of circumnuclear gas emission in early-type galaxies, revealing diverse gas structures and ionization mechanisms, and proposing a model involving low-velocity ionization cones aligned with gaseous discs.

Contribution

It provides detailed analysis of circumnuclear gas kinematics and ionization sources in a sample of 10 early-type galaxies, highlighting the presence of gaseous discs and ionization cones, and suggesting new insights into LINER emission.

Findings

Gaseous discs detected in 3 galaxies, with some showing non-Keplerian motions.

Presence of spiral structures and ionization bicones in specific galaxies.

Ionizing photons from AGN are insufficient to explain observed Hα flux, indicating additional ionization processes.

Abstract

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.