The Nature of Active Galactic Nuclei with Velocity Offset Emission Lines
  We obtained Keck/OSIRIS near-IR adaptive optics-assisted integral-field
spectroscopy to probe the morphology and kinematics of the ionized gas in four
velocity-offset active galactic nuclei (AGNs) from the Sloan Digital Sky
Survey. These objects possess optical emission lines that are offset in
velocity from systemic as measured from stellar absorption features. At a
resolution of ~0.18", OSIRIS allows us to distinguish which velocity offset
emission lines are produced by the motion of an AGN in a dual supermassive
black hole system, and which are produced by outflows or other kinematic
structures. In three galaxies, J1018+2941, J1055+1520 and J1346+5228, the
spectral offset of the emission lines is caused by AGN-driven outflows. In the
remaining galaxy, J1117+6140, a counterrotating nuclear disk is observed that
contains the peak of Pa$\alpha$ emission 0.2" from the center of the galaxy.
The most plausible explanation for the origin of this spatially and
kinematically offset peak is that it is a region of enhanced Pa$\alpha$
emission located at the intersection zone between the nuclear disk and the bar
of the galaxy. In all four objects, the peak of ionized gas emission is not
spatially coincident with the center of the galaxy as traced by the peak of the
near-IR continuum emission. The peaks of ionized gas emission are spatially
offset from the galaxy centers by 0.1"-0.4" (0.1-0.7 kpc). We find that the
velocity offset originates at the location of this peak of emission, and the
value of the offset can be directly measured in the velocity maps. The
emission-line ratios of these four velocity-offset AGNs can be reproduced only
with a mixture of shocks and AGN photoionization. Shocks provide a natural
explanation for the origin of the spatially and spectrally offset peaks of
ionized gas emission in these galaxies.
