THE MULTIPHASE STRUCTURE AND POWER SOURCES OF GALACTIC WINDS IN MAJOR MERGERS

Abstract

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