Astron. Astrophys. 339, 737-744 (1998)

¹³CO at the centre of M 82

N. Neininger ^{1, 2, 3}, M. Guélin ³, U. Klein ¹, S. García-Burillo ⁴ and R. Wielebinski <sup>2

1</sup> Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
³ Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, F-38406 St. Martin d'Hères, France
⁴ Observatorio Astronómico Nacional, Apartado 1143, E-28800 Alcalá de Henares, Spain

Received 14 August 1997 / Accepted 1 September 1998

Abstract

Using the IRAM interferometer, we have observed the nearby starburst galaxy M 82 with a resolution ( pc) in the 10 line of ¹³CO and in the 2.6-mm continuum.

The spatial distribution of the ¹³CO line shows the same gross features as the ¹²CO(10) map of Shen & Lo (1995), namely two lobes and a compact central source, though with different relative intensities. The lobes are more conspicuous and the central source is fainter in ¹³CO than in ¹²CO.

The velocity field observed around the nucleus shows a very steep gradient (140 km s^-1 over 75 pc), which is very probably caused by the stellar bar visible in the near infrared. The dynamical centre coincides with the IR peak and is shifted north-east of the compact ¹³CO source. The two CO lobes appear to be associated with the ends of the bar and not with a molecular ring, as usually assumed. They are probably shaped by the strong UV radiation from the central region. ¹³CO must be more photodissociated than the self-shielded ¹²CO molecules in the central 250 pc region, which may explain the relative weakness of the ¹³CO central source.

A 130 pc-wide bubble of molecular gas has been identified, which happens to host the most luminous compact radio source in M 82. It lies 120 pc west of the IR peak between the central source and the western lobe and seems characterized by warmer gas, strong UV radio free-free radiation, and an enhanced cosmic ray production rate.

Key words: ISM: bubbles galaxies: individual: M 82 galaxies: ISM galaxies: kinematics and dynamics galaxies: starburst radio lines: galaxies

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations and data reduction
• 3. Results
  • 3.1. Continuum emission at 110 GHz
  • 3.2. ¹³CO line emission
  • 3.3. Kinematics of the ¹³CO gas
• 4. A giant bubble
• 5. The fueling of the starburst
• 6. Summary and conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: October 22, 1998
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