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Title: REGIONAL VARIATIONS IN THE DENSE GAS HEATING AND COOLING IN M51 FROM HERSCHEL FAR-INFRARED SPECTROSCOPY

We present Herschel PACS and SPIRE spectroscopy of the most important far-infrared cooling lines in M51, [C II](158 μm), [N II](122 and 205 μm), [O I](63 and 145 μm), and [O III](88 μm). We compare the observed flux of these lines with the predicted flux from a photon-dominated region model to determine characteristics of the cold gas such as density, temperature, and the far-ultraviolet (FUV) radiation field, G{sub 0}, resolving details on physical scales of roughly 600 pc. We find an average [C II]/F{sub TIR} of 4 × 10{sup –3}, in agreement with previous studies of other galaxies. A pixel-by-pixel analysis of four distinct regions of M51 shows a radially decreasing trend in both the FUV radiation field, G{sub 0}, and the hydrogen density, n, peaking in the nucleus of the galaxy, and then falling off out to the arm and interarm regions. We see for the first time that the FUV flux and gas density are similar in the differing environments of the arm and interarm regions, suggesting that the inherent physical properties of the molecular clouds in both regions are essentially the same.
Authors:
; ; ;  [1] ; ;  [2] ; ;  [3] ;  [4] ;  [5] ;  [6] ; ; ;  [7] ;  [8] ;  [9]
  1. Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1 (Canada)
  2. Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, B-9000 Gent (Belgium)
  3. Laboratoire d'Astrophysique de Marseille-LAM, Université d'Aix-Marseille and CNRS, UMR7326, 38 rue F. Joliot-Curie, F-13388 Marseille Cedex 13 (France)
  4. Department of Physics and Astronomy, University of California, Irvine, CA 92697 (United States)
  5. Institut für Theoretische Astrophysik, Zentrum für Astronomie der Universität Heidelberg, Albert-Ueberle Str. 2, D-69120 Heidelberg (Germany)
  6. Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom)
  7. CEA, Laboratoire AIM, Irfu/SAp, Orme des Merisiers, F-91191 Gif-sur-Yvette (France)
  8. Institut d'Astrophysique de Paris, UMR7095 CNRS, Université Pierre and Marie Curie, 98 bis Boulevard Arago, F-75014 Paris (France)
  9. Istituto di Astrofisica e Planetologia Spaziali, INAF-IAPS, Via Fosso del Cavaliere 100, I-00133 Roma (Italy)
Publication Date:
OSTI Identifier:
22270749
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 776; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTROSCOPY; ASTRONOMY; ASTROPHYSICS; CARBON IONS; COMPARATIVE EVALUATIONS; DENSITY; FAR INFRARED RADIATION; FAR ULTRAVIOLET RADIATION; GALAXIES; GALAXY NUCLEI; HYDROGEN; INFRARED SPECTRA; NITROGEN IONS; PHOTONS; VARIATIONS