Cl and CO in the center of M 51

F. P. Israel, R. P.J. Tilanus, F. Baas

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


We present J = 2-1, J = 3-2, J = 4-3 12CO maps as well as J = 2-1, J = 3-2 13CO and 492 GHz [CI] measurements of the central region in M 51. The distribution of CO is strongly concentrated towards the spiral arms. The center itself is poor in, though not devoid of, CO emission. The observed line intensities require modelling with a multi-component molecular gas. A dense component must be present (n(H2) ≈ 10 3) with kinetic temperature Tkin ≈ 100 K, combined with either a less dense (≈ 102 cm-3) component of the same temperature, or a more dense (n(H2) ≈ 3 × 10 3 cm-3) and much cooler (Tkin = 10-30 K) component. Atomic carbon amounts are between 5 and 10 times those of CO. Much of the molecular gas mass is associated with the hot PDR phase. The center of M 51 has a face-on gas mass density of about 40 ± 20 M pc-2, and a well-established CO-to-H2 conversion ratio X four to five times lower than the standard Galactic value.

Original languageEnglish (US)
Pages (from-to)907-913
Number of pages7
JournalAstronomy and astrophysics
Issue number3
StatePublished - Jan 2006
Externally publishedYes


  • Galaxies: ISM
  • Galaxies: individual: M 51
  • Galaxies: nuclei
  • Galaxies: spiral
  • Submillimeter

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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