Origin and Dynamical Support of Ionized Gas in Galaxy Bulges
  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.
