ISO Far-IR spectroscopy of IR-bright galaxies and ULIRGs |
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| Authors: | J. Fischer M.L. Luhman S. Satyapal M.A. Greenhouse G.J. Stacey C.M. Bradford S.D. Lord J.R. Brauher S.J. Unger P.E. Clegg H.A. Smith G. Melnick J.W. Colbert M.A. Malkan L. Spinoglio P. Cox V. Harvey J.-P Suter V. Strelnitski |
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| Affiliation: | (1) Naval Research Laboratory, Washington, DC, USA;(2) NASA Goddard Space Flight Center, Greenbelt, MD, USA;(3) Astronomy Department, Cornell University, Ithaca, NY, USA;(4) California Institute of Technology, IPAC, Pasadena, CA, USA;(5) ueen Mary & Westfield College, Univ. of London, London, UK;(6) Harvard-Smithsonian, CfA, Cambridge, MA, USA;(7) Dept. of Astronomy, Univ. of California, Los Angeles, CA, USA;(8) Istituto di Fisica dello Spazio Interplanetario-CNR, Roma, Italy;(9) Institut d'Astronomie Spatiale, Orsay, France;(10) Maria Mitchell Observatory, Nantucket, MA, USA |
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| Abstract: | Based on far-infrared spectroscopy of a small sample of nearbyinfrared-bright and ultraluminous infrared galaxies (ULIRGs) with theISO Long Wavelength Spectrometer we find adramatic progression in ionic/atomic fine-structure emission line andmolecular/atomic absorption line characteristics in these galaxiesextending from strong [O III]52,88  m and [N III]57 m lineemission to detection of only faint [C II]158 m line emissionfrom gas in photodissociation regions in the ULIRGs. The molecularabsorption spectra show varying excitation as well, extending fromgalaxies in which the molecular population mainly occupies the groundstate to galaxies in which there is significant population in higherlevels. In the case of the prototypical ULIRG, the merger galaxy Arp220, the spectrum is dominated by absorption lines of OH, H2O, CH,and [O I]. Low [O III]88 m line flux relative to the integratedfar-infrared flux correlates with low excitation and does not appear tobe due to far-infrared extinction or to density effects. A progressiontoward soft radiation fields or very dusty H II regions may explainthese effects. |
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| Keywords: | infrared-bright galaxies ultraluminous galaxies far-infrared spectra starbursts interstellar medium |
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