Origin and Dynamical Support of Ionized Gas in Galaxy Bulges

TL;DR

This study investigates the dynamical state and physical origin of ionized gas in galaxy bulges by analyzing velocity dispersions, revealing correlations with stellar motions, effects of AGN activity, and implications for galaxy evolution models.

Contribution

It provides new insights into the relationship between ionized gas and stellar kinematics, and the impact of AGN feedback on gas dynamics in galaxy bulges.

Findings

Gas velocity dispersions correlate with stellar dispersions (sigma_g/sigma_* ~ 0.6-1.4).

Gas kinematics reflect the hot gas velocity field in bulges.

AGN activity influences gas velocity dispersion and line luminosity correlation.

Abstract

We combine ionized gas ([N II] 6583) and stellar central velocity dispersions for a sample of 345 galaxies, with and without active galactic nuclei (AGNs), to study the dynamical state of the nuclear gas and its physical origin. The gas dispersions strongly correlate with the stellar dispersions over the velocity range of 30-350 km/s such that sigma_g/sigma_* ~ 0.6-1.4, with an average value of 0.80. These results are independent of Hubble type (for galaxies from E to Sbc), presence or absence of a bar, or local galaxy environment. For galaxies of type Sc and later and that have sigma_* < 40 km/s, the gas seems to have a minimum threshold of sigma_g ~ 30 km/s, such that sigma_g/sigma_* always exceeds 1. Within the sample of AGNs, sigma_g/sigma_* increases with nuclear luminosity or Eddington ratio, a possible manifestation of AGN feedback associated with accretion disk winds or outflows. This extra source of nongravitational line broadening should be removed when trying to use sigma_g to estimate sigma_*. We show that the mass budget of the narrow-line region can be accounted for by mass loss from evolved stars. The kinematics of the gas, dominated by random motions, largely reflect the velocity field of the hot gas in the bulge. Lastly, we offer a simple explanation for the correlation between line width and line luminosity observed in the narrow-line region of AGNs.