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Insights into gas heating and cooling in the disc of NGC 891 from Herschel far-infrared spectroscopy

Hughes, T. M. and Foyle, K. and Schirm, M. R. P. and Parkin, T. J. and De Looze, I. and Wilson, C. D. and Bendo, G. J. and Baes, M. and Fritz, J. and Boselli, A. and Cooray, A. and Cormier, D. and Karczewski, O. Ł. and Lebouteiller, V. and Lu, N. and Madden, S. C. and Spinoglio, L. and Viaene, S. (2015) Insights into gas heating and cooling in the disc of NGC 891 from Herschel far-infrared spectroscopy. Astronomy and Astrophysics, 517 . Art. No. A17. ISSN 0004-6361.

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We present Herschel PACS and SPIRE spectroscopy of the most important far-infrared cooling lines in the nearby, edge-on spiral galaxy, NGC 891: [Cii] 158 μm, [Nii] 122, 205 μm, [Oi] 63, 145 μm, and [Oiii] 88 μm. We find that the photoelectric heating efficiency of the gas, traced via the ([Cii]+[Oi]63)/FTIR ratio, varies from a mean of 3.5 × 10^(-3) in the centre up to 8 × 10^(-3) at increasing radial and vertical distances in the disc. A decrease in ([Cii]+[Oi]63)/F_(TIR) but constant ([Cii]+[Oi]63)/F_(PAH) with increasing FIR colour suggests that polycyclic aromatic hydrocarbons (PAHs) may become important for gas heating in the central regions. We compare the observed flux of the FIR cooling lines and total IR emission with the predicted flux from a PDR model to determine the gas density, surface temperature and the strength of the incident far-ultraviolet (FUV) radiation field, G0. Resolving details on physical scales of ~0.6 kpc, a pixel-by-pixel analysis reveals that the majority of the PDRs in NGC 891’s disc have hydrogen densities of 1 < log (n/ cm^(-3)) < 3.5 experiencing an incident FUV radiation field with strengths of 1.7 < log G_0< 3. Although these values we derive for most of the disc are consistent with the gas properties found in PDRs in the spiral arms and inter-arm regions of M 51, observed radial trends in n and G_0 are shown to be sensitive to varying optical thickness in the lines, demonstrating the importance of accurately accounting for optical depth effects when interpreting observations of high inclination systems. Increasing the coverage of our analysis by using an empirical relationship between the MIPS 24 μm and [Nii] 205 μm emission, we estimate an enhancement of the FUV radiation field strength in the far north-eastern side of the disc relative to the rest of the disc that coincides with the above-average star formation rate surface densities and gas-to-dust ratios. However, an accurate interpretation remains difficult due to optical depth effects, confusion along the line-of-sight and observational uncertainties.

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URLURL TypeDescription Paper
Wilson, C. D.0000-0001-5817-0991
Cooray, A.0000-0002-3892-0190
Lu, N.0000-0002-8948-1044
Additional Information:© 2015 ESO. Received 1 August 2014. Accepted 21 October 2014. We thank the referee for useful comments and suggestions which significantly improved the quality of this paper. T.M.H. gratefully acknowledges the financial support from the Belgian Science Policy Office (BELSPO) in the frame of the PRODEX project C90370 (Herschel PACS guaranteed time and open time programs: science exploitation). I.D.L. is a postdoctoral fellow of the Flemish Fund for Scientific Research (FWO Vlaanderen). M.B. also acknowledges the financial support of the same Flemish Fund for Scientific Research. PACS has been developed by a consortium of institutes led by MPE (Germany) and including UVIE (Austria); KU Leuven, CSL, IMEC (Belgium); CEA, LAM (France); MPIA (Germany); INAF-IFSI/OAA/OAP/OAT, LENS, SISSA (Italy); IAC (Spain). This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI/INAF (Italy), and CICYT/MCYT (Spain). SPIRE has been developed by a consortium of institutes led by Cardiff University (UK) and including Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK); and NASA (USA). This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the NASA (USA). This research made use of APLpy, an open-source plotting package for Python hosted at http: //, and Montage, which is funded by the NASA (USA) Earth Science Technology Office, Computation Technologies Project, under Cooperative Agreement Number NCC5-626 between NASA and Caltech, and maintained by the NASA/IPAC Infrared Science Archive.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Belgian Science Policy Office (BELSPO) PRODEXC90370
Fonds Wetenschappelijk Onderzoek - Vlaanderen (FWO)UNSPECIFIED
Bundesministerium für Verkehr, Innovation und Technologie (BMVIT)UNSPECIFIED
Commissariat à l’Energie Atomique (CEA)UNSPECIFIED
Deutsches Zentrum für Luft- und Raumfahrt (DLR)UNSPECIFIED
Agenzia Spaziale Italiana (ASI)UNSPECIFIED
Canadian Space Agency (CSA)UNSPECIFIED
National Astronomical Observatories, Chinese Academy of Sciences (NAOC)UNSPECIFIED
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Ministerio de Ciencia e Innovación (MCINN)UNSPECIFIED
Swedish National Space Board (SNSB)UNSPECIFIED
Science and Technology Facilities Council (STFC)UNSPECIFIED
United Kingdom Space Agency (UKSA)UNSPECIFIED
Centre National d'Études Spatiales (CNES)UNSPECIFIED
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Subject Keywords:galaxies: individual: NGC 891, galaxies: spiral, galaxies: ISM, infrared: galaxies, ISM: lines and bands
Record Number:CaltechAUTHORS:20150410-081122333
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Official Citation:T. M. Hughes, K. Foyle, M. R. P. Schirm, T. J. Parkin, I. De Looze, C. D. Wilson, G. J. Bendo, M. Baes, J. Fritz, A. Boselli, A. Cooray, D. Cormier, O. Ł. Karczewski, V. Lebouteiller, N. Lu, S. C. Madden, L. Spinoglio and S. Viaene A&A 575 A17 (2015) DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56565
Deposited By: Ruth Sustaita
Deposited On:10 Apr 2015 16:33
Last Modified:09 Mar 2020 13:19

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