Velocity resolved HIFI spectroscopy of water lines in actively starforming galaxies

Recent Herschel spectroscopy has shown that water lines can be veryprominent in the submm spectra of infrared (IR) bright galacticnuclei. Water can efficiently be excited by the IR photons of the dustcontinuum and via collisions of shockheated gas in starformingregions. In the later case H _2 O contributes significantly to the gascooling. So far, the relative importance of the processes driving thewater excitation are largely unknown. This is mainly because the submmlines of water in extragalactic systems have only become accessiblewith the launch of Herschel. Our first velocityresolved HIFI spectroscopy of lowlevel watertransitions in actively starforming galaxies shows that water lineprofiles are formed by a mix of emission and absorption features andthat the line profiles strongly vary between different watertransitions. This shows that a lot of information on the underlyingISM structure is imprinted on the line profiles. On the other handthis implies, that velocity resolved spectroscopy is required in orderto investigate the water excitation and the underlying physicalconditions of the ISM.We here propose to observe a set of five medium and high energy waterlines using HIFI in a sample of active galaxies which arerepresentative for a wide range of nuclear environments. Inconjunction with the lowlevel water lines form the HEXGAL GTKP thisline selection will allow us to model the water excitation inoutstanding detail and to investigate the relative contribution of thewater excitation channels as a function of environment, derivechemical abundances and to investigate the underlying physicalparameters of the gas. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]