Recent Herschel spectroscopy has shown that water lines can be veryprominent in the submm spectra of infra-red (IR) bright galacticnuclei. Water can efficiently be excited by the IR photons of the dustcontinuum and via collisions of shock-heated 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 velocity-resolved HIFI spectroscopy of low-level 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 low-level water lines form the HEXGAL GT-KP 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.
Publication
HIFI Spectroscopy of H2O Submillimeter Lines in Nuclei of Actively Star-forming Galaxies | Liu L. et al. | The Astrophysical Journal Volume 846 Issue 1 article id. 5 35 pp. (2017). | 846 | 10.3847/1538-4357/aa81b4 | 2017ApJ...846....5L | http://adsabs.harvard.edu/abs/2017ApJ...846....5L
Instrument
HIFI_HifiPoint_dbs
Temporal Coverage
2011-06-09T00:10:14Z/2012-09-20T05:55:15Z
Version
SPG v14.1.0
Mission Description
Herschel was launched on 14 May 2009! It is the fourth cornerstone mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
European Space Agency, weiss et al., 2013, 'Velocity resolved HIFI spectroscopy of water lines in actively starforming galaxies', SPG v14.1.0, European Space Agency, https://doi.org/10.5270/esa-lx5783g
