Mapping Large-Scale Gaseous Outflows in Ultraluminous Infrared Galaxies   with Keck II ESI Spectra: Spatial Extent of the Outflow
  The kinematics of neutral gas and warm ionized gas have been mapped in one-dimension across ultraluminous starburst galaxies using interstellar absorption and emission lines, in Keck II ESI spectra. Blue-shifted absorption is found along more of the slit than anticipated, exceeding scales of 15 kpc across several systems. The large velocity gradient measured across some of these outflows is inconsistent with a flow diverging from the central starburst -- angular momentum conservation reduces the rotational velocity of an outflow as it expands. More widespread star formation, likely triggered by the merger, probably drives these outflows, although some models suggest the collision itself could generate a wind by shock heating interstellar gas throughout the disk. Young mergers with separated nuclei present the highest outflow masses, due mainly to the larger area over which the cool gas can be detected. In a typical ULIG, the mass carried by the cool phase of the outflow is around 10^8Msun, or a few percent of the total dynamical mass. Assuming the starburst activity has proceeded at the observed rate for the past 10 Myr, the kinetic energy of the cool outflows is a few percent of the supernova energy, consistent with starbursts powering the outflows. The cool wind is expected to be accelerated by momentum deposition, possibly from radiation pressure as well as supernovae. Such models imply turn-around radii for the cool outflows of at least 30 to 90 kpc. This cross-section presents a significant NaI absorption cross section. If most L > 0.1L* galaxies pass through a luminous starburst phase, then relics of cool outflows will create a significant redshift-path density. Galaxy formation models should include this cool phase of the outflow in addition to a hot wind in feedback models. 
Crystal L. Martin (UCSB)