The water abundance behind interstellar shocks: results from $Herschel$/PACS and $Spitzer$/IRS observations of H${}_2$O, CO, and H${}_2$

Abstract

We have investigated the water abundance in shock-heated molecular gas, making use of $Herschel$ measurements of far-infrared CO and H${}_2$O line emissions in combination with $Spitzer$ measurements of mid-IR H${}_2$ rotational emissions. We present far-infrared line spectra obtained with $Herschel$'s PACS instrument in range spectroscopy mode towards two positions in the protostellar outflow NGC 2071 and one position each in the supernova remnants W28 and 3C391. These spectra provide unequivocal detections, at one or more positions, of 12 rotational lines of water, 14 rotational lines of CO, 8 rotational lines of OH (4 lambda doublets), and 7 fine-structure transitions of atoms or atomic ions. We first used a simultaneous fit to the CO line fluxes, along with H${}_2$ rotational line fluxes measured previously by $Spitzer$, to constrain the temperature and density distribution within the emitting gas; and we then investigated the water abundances implied by the observed H${}_2$O line fluxes. The water line fluxes are in acceptable agreement with standard theoretical models for nondissociative shocks that predict the complete vaporization of grain mantles in shocks of velocity $v\sim 25$ km/s, behind which the characteristic gas temperature is $\sim 1300$ K and the H${}_2$O/CO ratio is 1.2

42 pages, 15 figures, accepted for publication in the Astrophysical Journal

References in corpus (6)

• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• Interstellar water chemistry: from laboratory to observations
• Parametrization of C-shocks. Evolution of the Sputtering of Grains
• Spitzer observations of HH54 and HH7-11: mapping the H2 ortho-to-para ratio in shocked molecular gas
• Spitzer spectral line mapping of supernova remnants: I. Basic data and principal component analysis
• Detection of Extended Hot Water in the Outflow from NGC 2071

Cited by in corpus (17)

• Water in star-forming regions (WISH): Physics and chemistry from clouds to disks as probed by Herschel spectroscopy
• Interstellar Hydrides
• The chemistry and spatial distribution of small hydrocarbons in UV-irradiated molecular clouds: the Orion Bar PDR
• The Herschel-PACS legacy of low-mass protostars: Properties of warm and hot gas and its origin in far-UV illuminated shocks
• Herschel Far-Infrared Spectral-mapping of Orion BN/KL Outflows: Spatial distribution of excited CO, H2O, OH, O and C+ in shocked gas
• Asymmetric supernova remnants generated by Galactic, massive runaway stars
• Gas phase Elemental abundances in Molecular cloudS (GEMS) VI. A sulphur journey across star-forming regions: study of thioformaldehyde emission
• Linking low- to high-mass YSOs with Herschel-HIFI observations of water
• Collisional excitation of water by hydrogen atoms
• Molecular line study of the S-type AGB star W Aquilae. ALMA observations of CS, SiS, SiO and HCN
• The Herschel-HIFI view of mid-IR quiet massive protostellar objects
• H${}_2$ emission from non-stationary magnetized bow shocks
• Herschel Key Program, "Dust, Ice, and Gas In Time" (DIGIT): the origin of molecular and atomic emission in low-mass protostars in Taurus
• Discovery of Broad Molecular lines and of Shocked Molecular Hydrogen from the Supernova Remnant G357.7+0.3: HHSMT, APEX, Spitzer and SOFIA Observations
• Far infrared CO and H${}_2$O emission in intermediate-mass protostars
• Molecular Oxygen in the nearest QSO Mrk 231
• Supernova Shocks in Molecular Clouds: Shocks Driven into Dense Cores in IC 443 and 3C 391