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 {\mu}m)
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 12CO and 13CO lines strongly indicates a very warm
molecular gas component at ~500 K and pressure of ~3x10^6 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.
