| Description |
One of the exciting new results of the Herschel mission is the discovery of massive, high velocity (v ~ 1000 km/sec) molecular outflows in ultraluminous infrared galaxies (ULIRGs). These outflows, powered by stellar processes or by AGN, are so far, best traced by radiatively pumped far-IR OH transitions and are observed in numerous transitions as P-Cygni, absorption, or emission line profiles. Based on our modeling of the lines and continuum, the OH observations imply short gas depletion times, mass loss rates at least several times higher than the star formation rates, and appear strongest in AGN dominated ULIRGs. These mergers of gas-rich galaxies have been caught in the act of dispersing their star-forming molecular fuel as they evolve toward becoming massive, gas-poor ellipticals! Are these outflows driven by radio jets or radiation pressure due to a partially buried AGN or are compact super-starburst winds carving out a view to a previously hidden AGN? We and others have tuned Herschel PACS spectroscopic scans to one or more OH lines in surveys of infrared-bright galaxies to combine with modeling efforts to derive the parameters of these winds. However, in order to help understand the excitation and radiative effects producing these winds and thus to better ascertain the nature of the driving source(s), we propose to fill in the gaps and thus obtain full PACS spectral scans of two key outflow sources: Mrk 231, a broad absorption line (BAL) quasar, and NGC 6240, a close pair of X-ray luminous AGN. The PACS spectral resolution and sensitivity will enable unprecedented understanding of the outflow mass-loss rates, energetics, and the radiative environments to which their ISM is exposed, based on velocity-resolved line profiles of multiple excited level transitions of OH, H2O, CO, OH+, H2O+, and other molecules. A key goal of this program is to provide foundations for the modeling and understanding of the now numerous Herschel OH outflow surveys of ULIRGs. |
