Astron. Astrophys. 358, 65-71 (2000)

Cold dust in the starburst galaxy M 82

G. Thuma ¹, N. Neininger ², U. Klein ² and R. Wielebinski <sup>1

1</sup> Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
² Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany

Received 22 October 1999 / Accepted 3 April 2000

Abstract

The starburst galaxy M 82 has been mapped at 1.2 mm using the IRAM 30-m telescope and the MPIfR 19-channel bolometer. The influence of the sidelobe pattern and the ¹²CO(2-1) line has been carefully analyzed. Based on this analysis, we conclude that the cold dust does not extend far into the halo as has been previously claimed. The total mass of dust in the inner 3 kpc of the galaxy is . Assuming a solar gas-to-dust ratio, the inferred total mass of gas is   .

Unlike in any other galaxy we find the CO(2-1) line emission to be clearly more extended than the 1.2 mm dust emission. A likely explanation for this exceptional behaviour, seen for the first time in galaxies, is heating of molecular gas by low-energy cosmic rays and soft X-rays in the halo of M 82.

Key words: ISM: dust, extinction galaxies: individual: M 82 galaxies: ISM galaxies: starburst radio continuum: galaxies radio continuum: ISM

Send offprint requests to: G. Thuma (gthuma@mpifr-bonn.mpg.de)

© European Southern Observatory (ESO) 2000

Online publication: June 26, 2000

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