The Inner Kiloparsec of Mrk 273 with Keck Adaptive Optics
  There is X-ray, optical, and mid-infrared imaging and spectroscopic evidence
that the late-stage ultraluminous infrared galaxy merger Mrk 273 hosts a
powerful active galactic nucleus (AGN). However, the exact location of the AGN
and the nature of the nuclei have been difficult to determine due to dust
obscuration and the limited wavelength coverage of available high-resolution
data. Here we present near-infrared integral-field spectra and images of the
nuclear region of Mrk 273 taken with OSIRIS and NIRC2 on the Keck II Telescope
with laser guide star adaptive optics. We observe three spatially resolved
components, and analyze the local molecular and ionized gas emission lines and
their kinematics. We confirm the presence of the hard X-ray AGN in the
southwest nucleus. In the north nucleus, we find a strongly rotating gas disk
whose kinematics indicate a central black hole of mass 1.04 +/- 0.1 x 10^9
Msun. The H2 emission line shows an increase in velocity dispersion along the
minor axis in both directions, and an increased flux with negative velocities
in the southeast direction; this provides direct evidence for a collimated
molecular outflow along the axis of rotation of the disk. The third spatially
distinct component appears to the southeast, 640 and 750 pc from the north and
southwest nuclei, respectively. This component is faint in continuum emission
but shows several strong emission line features, including [Si vi] 1.964 {\mu}m
which traces an extended coronal-line region. The geometry of the [Si vi]
emission combined with shock models and energy arguments suggest that [Si vi]
in the southeast component must be at least partly ionized by the SW AGN or a
putative AGN in the northern disk, either through photoionization or through
shock-heating from strong AGN- and circumnuclear starburst-driven outflows.
This lends support to a scenario in which Mrk 273 may be a dual AGN system.
