Description |
H2O and OH are key tracers of the structure, kinematics, and activity in the nuclear regions of (Ultra) Luminous Infrared Galaxies (ULIRGs): with their excitation dominated by pumping by far-infrared continuum radiation, they probe the nuclear source of the far-IR radiation and its associated structures (disks, torus); their P-Cygni, absorption, and emission profiles trace massive molecular outflows and possibly inflows, and the astrophysically important associated energetics involved in the (negative) feedback from star formation and/or AGN on the molecular gas; they probe the physical and radiative environments (X-rays, cosmic rays, hot cores) where they reside. In order to distinguish among the above scenarios, we propose PACS spectroscopy of key transitions of H2O and OH in a sample of 9 bright (U)LIRGs where submillimeter H2O lines have been detected with SPIRE, as well as key diagnostic lines of NH3 and OH+ to ascertain the formation mechanism and implied physical processes. The proposed observations will serve as a crucial benchmark for future routine observations of H2O with ALMA in the distant Universe. |