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Published July 2010 | Published
Journal Article Open

Probing the molecular interstellar medium of M82 with Herschel-SPIRE spectroscopy


We present the observations of the starburst galaxy M82 taken with the Herschel SPIRE Fourier-transform spectrometer. The spectrum (194–671 μm) shows a prominent CO rotational ladder from J = 4–3 to 13–12 emitted by the central region of M82. The fundamental properties of the gas are well constrained by the high J lines observed for the first time. Radiative transfer modeling of these high-S/N ^(12)CO and ^(13)CO lines strongly indicates a very warm molecular gas component at ~500 K and pressure of ~3×10^6 K cm^(-3), in good agreement with the H_2 rotational lines measurements from Spitzer and ISO. We suggest that this warm gas is heated by dissipation of turbulence in the interstellar medium (ISM) rather than X-rays or UV flux from the straburst. This paper illustrates the promise of the SPIRE FTS for the study of the ISM of nearby galaxies.

Additional Information

© 2010 ESO. Received 30 March 2010; Accepted 28 April 2010; Published online 16 July 2010. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. We are grateful to P. Maloney for his advices on radiative transfer modeling, and to the SPIRE FTS team for assistance with data reduction. SPIRE has been developed by a consortium of institutes led by Cardiff University (UK) and including Univ. Lethbridge (Canada); NAOC (China); CEA, OAMP (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech/JPL, IPAC, 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 (UK); and NASA (USA). Additional funding support for some instrument activities has been provided by ESA.

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