Stars and ionized gas in S0 galaxy NGC 7743: an inclined large-scale gaseous disk

TL;DR

This study reveals an inclined large-scale gaseous disk in NGC 7743 formed likely through external gas accretion, with ionized gas dynamics and excitation dominated by shocks and AGN activity.

Contribution

It provides detailed kinematic and ionization analysis of the inclined gaseous disk in NGC 7743, highlighting its external origin and shock-dominated ionization.

Findings

Ionized gas forms a significantly inclined disk relative to the stellar disk.

The inclined disk likely originated from external gas accretion from a satellite.

Shock waves dominate the ionization state of the gaseous disk.

Abstract

We used deep long-slit spectra and integral-field spectral data to study the stars and ionized gas kinematics and stellar population properties in the lenticular barred galaxy NGC 7743. We have shown that ionized gas at the distances larger than 1.5 kpc from the nucleus settles in the disk which is significantly inclined to the stellar disk of the galaxy. Making different assumptions about the geometry of the disks and involving different sets of emission lines into the fitting, under the assumption of thin flat disk circular rotation, we obtain the full possible range of angle between the disks to be 34+/-9 or 77+/-9 deg. The most probable origin of the inclined disk is the external gas accretion from a satellite, orbiting the host galaxy with a corresponding angular momentum direction. The published data on the HI distribution around NGC 7743 suggest that the galaxy has a gas-rich environment. The emission-line ratio diagrams imply the domination of shock waves in the ionization state of the gaseous disk, whereas the contribution of photoionization by recent star formation seems to be negligible. In some parts of the disk a difference between the velocities of the gas emitting in the forbidden lines and in the Balmer lines is detected. It may be caused by the fact that the inclined disk is mainly shock-excited, whereas some fraction of the Balmer-line emission is produced by a small amount of gas excited by young stars in the main stellar disk of NGC 7743. In the circumnuclear region (R< 200 pc) some evidences of the AGN jet interaction with an ambient interstellar medium were found.