The Multiphase Structure and Power Sources of Galactic Winds in Major
  Mergers
  Massive, galaxy-scale outflows are known to be ubiquitous in major mergers of
disk galaxies in the local universe. In this paper, we explore the multiphase
structure and power sources of galactic winds in six ultraluminous infrared
galaxies (ULIRGs) at z < 0.06 using deep integral field spectroscopy with the
Gemini Multi-Object Spectrograph (GMOS) on Gemini North. We probe the neutral,
ionized, and dusty gas phases using Na I D, strong emission lines ([O I],
Halpha, and [N II]), and continuum colors, respectively. We separate outflow
motions from those due to rotation and tidal perturbations, and find that all
of the galaxies in our sample host high-velocity flows on kiloparsec scales.
The properties of these outflows are consistent with multiphase (ionized,
neutral, and dusty) collimated bipolar winds emerging along the minor axis of
the nuclear disk to scales of 1-2 kpc. In two cases, these collimated winds
take the form of bipolar superbubbles, identified by clear kinematic
signatures. Less collimated (but still high-velocity) flows are also present on
scales up to 5 kpc in most systems. The three galaxies in our sample with
obscured QSOs host higher velocity outflows than those in the three galaxies
with no evidence for an AGN. The peak outflow velocity in each of the QSOs is
in the range 1450-3350 km/s, and the highest velocities (2000-3000 km/s) are
seen only in ionized gas. The outflow energy and momentum in the QSOs are
difficult to produce from a starburst alone, but are consistent with the QSO
contributing significantly to the driving of the flow. Finally, when all gas
phases are accounted for, the outflows are massive enough to provide negative
feedback to star formation.
