Program: GN-2007A-Q-107

Recent large surveys of the \nad\ absorption-line feature in infrared-luminous galaxies reveal extended, massive outflows of neutral gas and dust in all of these galaxies. The impact of these winds on the evolution of galaxies, intergalactic gas, and supermassive black holes is substantial, as infrared-luminous galaxies host most of the star formation in the universe at $z > 1$. However, important questions remain about the structure and power source of the winds in the most powerful of these galaxies, the ultraluminous infrared galaxies (ULIRGs). We propose to map the interstellar absorption lines in two of the nearest and brightest ULIRGs using the integral field unit of GMOS on Gemini North. Our two targets are already known to possess spatial variations in \nad\ from long-slit observations. The GMOS IFU will allow us to observe the projected three-dimensional structure of these winds, which is highly uncertain. 3-D spectroscopy will determine if the winds have small or large opening angles, and, through modeling of the velocity field, if a standard wind models fit the data. This will allow much better determinations of mass and energy in the wind, which depend sensitively on wind geometry. The structure of the wind is finally relevant to its power source, which in starburst/active galactic nucleus composite ULIRGs is uncertain from long-slit observations. Confirming hints of a jet signature in Mrk~231, which would be a ``smoking-gun'' signature of AGN-driving, will be easily distinguished from wide-angle outflows in the GMOS data.