Origin and dynamical support of ionized gas in galaxy bulges

Abstract

We combine ionized gas ([NII] λ6583) 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 σ 30-350kms-1, such that σg/σ* 0.6-1.4, with an average value of 0.80. These results are independent of Hubble type (for galaxies from E to Sbc), the presence or absence of a bar, or local galaxy environment. For galaxies of type Sc and later and that have σ* ≲ 40km s -1, the gas seems to have a minimum threshold of σg 30km s-1, such that σg/σ* always exceeds 1. Within the sample of AGNs, σg/σ * 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 σg to estimate σ *. We show that the mass budget of the narrow-line region (NLR) 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 NLR of AGNs. © 2009. The American Astronomical Society.