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Article Dans Une Revue Astronomy and Astrophysics - A&A Année : 2010

Herschel observations of water vapour in Markarian 231

1 Departamente de Física, Universidad de Alcalá Henares
2 Remote Sensing Division, Naval Research laboratory
3 Astrophysics Division, European Space Agency (ESA)
4 UCL - University College of London [London]
5 University of Groningen [Groningen]
6 Leiden Observatory
7 Harvard-Smithsonian Center for Astrophysics
8 Crete Center for Theoretical Physics, Department of Physics
9 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
10 OSO - Onsala Space Observatory, Chalmers University of Technology
11 MPIfR - Max-Planck-Institut für Radioastronomie
12 MPIA - Max-Planck-Institut für Astronomie
13 CAB - Centro de Astrobiología, Consejo Superior de Investigaciones Científicas (CSIC)/Instituto Nacional de Técnica Aeroespacial (INTA)
14 Space Astronomy Division, Institute for Space Imaging Science, Department of Physics and Astronomy, University of Lethbridge
15 IFSI - Istituto di Fisica dello Spazio Interplanetario
16 Department of Astronomy, University of Maryland
17 IPAC - Infrared Processing Analysis Center, California Institute of Technology
18 Institute of Astronomy and Astrophysics, National Observatory of Athens
19 Institute for Astronomy, University of Hawaii
20 CEA - Commissariat à l'énergie atomique et aux énergies alternatives
21 IRAM - Instituto de Radio Astronomía Milimétrica
22 Rheinische Friedrich-Wilhelms-Universität Bonn
23 Department of Astronomy, Cornell University
24 Astronomy Department, University of Virginia, Charlottesville
25 Purple Mountain Observatory
R. Meijerink
  • Fonction : Auteur
A. F. Loenen
  • Fonction : Auteur
C. Vlahakis
  • Fonction : Auteur

Résumé

The Ultra luminous infrared galaxy (ULIRG) Mrk 231 reveals up to seven rotational lines of water (H2O) in emission, including a very high-lying (Eupper = 640 K) line detected at a 4sigma level, within the Herschel/SPIRE wavelength range (190 < lambda (mum) < 640), whereas PACS observations show one H2O line at 78 mum in absorption, as found for other H2O lines previously detected by ISO. The absorption/emission dichotomy is caused by the pumping of the rotational levels by far-infrared radiation emitted by dust, and subsequent relaxation through lines at longer wavelengths, which allows us to estimate both the column density of H2O and the general characteristics of the underlying far-infrared continuum source. Radiative transfer models including excitation through both absorption of far-infrared radiation emitted by dust and collisions are used to calculate the equilibrium level populations of H2O and the corresponding line fluxes. The highest-lying H2O lines detected in emission, with levels at 300-640 K above the ground state, indicate that the source of far-infrared radiation responsible for the pumping is compact (radius = 110-180 pc) and warm (Tdust = 85-95 K), accounting for at least 45% of the bolometric luminosity. The high column density, N(H2O) ~ 5×1017 cm-2, found in this nuclear component, is most probably the consequence of shocks/cosmic rays, an XDR chemistry, and/or an ``undepleted chemistry'' where grain mantles are evaporated. A more extended region, presumably the inner region of the 1-kpc disk observed in other molecular species, could contribute to the flux observed in low-lying H2O lines through dense hot cores, and/or shocks. The H2O 78 mum line observed with PACS shows hints of a blue-shifted wing seen in absorption, possibly indicating the occurrence of H2O in the prominent outflow detected in OH (Fischer et al. 2010, A&A, 518, L41). Additional PACS/HIFI observations of H2O lines are required to constrain the kinematics of the nuclear component, as well as the distribution of H2O relative to the warm dust.

Dates et versions

hal-03742334 , version 1 (02-08-2022)

Identifiants

Citer

Eduardo González-Alfonso, J. Fischer, Kate J. Isaak, A. Rykala, Giorgio Savini, et al.. Herschel observations of water vapour in Markarian 231. Astronomy and Astrophysics - A&A, 2010, 518, pp.L43. ⟨10.1051/0004-6361/201014664⟩. ⟨hal-03742334⟩
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