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Astron. Astrophys. 345, L23-L26 (1999)

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Letter to the Editor

Evidence for an expanding molecular superbubble in M 82

Axel Weiß, Fabian Walter, Nikolaus Neininger and Uli Klein

Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany

Received 23 February 1999 / Accepted 6 April 1999


We present evidence for an expanding superbubble in M 82 (diameter: [FORMULA] 130 pc, expansion velocity: [FORMULA] 45 km s-1, mass: [FORMULA]M[FORMULA]). It is seen in the [FORMULA], [FORMULA], [FORMULA] and [FORMULA] lines. The superbubble is centred around the most powerful supernova remnant, 41.9+58. The CO observations show that the molecular superbubble already broke out of the disk. This scenario is supported by ROSAT HRI observations which suggest that hot coronal gas originating from inside the shell is the main contributor to the diffuse X-ray outflow in M 82. We briefly discuss observations of the same region at other wavelengths (radio continuum, optical, H I , X-rays, ionized gas). From our spectral line observations, we derive a kinematic age of about [FORMULA] years for the superbubble. Using simple theoretical models, the total energy needed for the creation of this superbubble is of order [FORMULA]ergs. The required energy input rate (0.001 SN yr-1) is reasonable given the high supernova (SN) rate of [FORMULA] SN yr-1 in the central part of M 82. As much as 10% of the energy needed to create the superbubble is still present in form of the kinetic energy of the expanding molecular shell. Of order 10% is conserved in the hot X-ray emitting gas emerging from the superbubble into the halo of M 82. This newly detected expanding molecular superbubble is believed to be powered by the same objects that also lie at the origin of the prominent X-ray outflow in M 82. It can therefore be used as an alternative tool to investigate the physical properties of these sources.

Key words: ISM: bubbles – galaxies: individual: M 82 – galaxies: ISM – galaxies: kinematics and dynamics – galaxies: starburst – X-rays: ISM

Send offprint requests to: A.Weiß(aweiss@astro.uni-bonn.de)

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© European Southern Observatory (ESO) 1999

Online publication: April 19, 1999