Evidence for an expanding molecular superbubble in M 82

We present evidence for an expanding superbubble in M 82 (diameter: approxi mate to 130 pc, expansion velocity: approximate to 45 km s-1, mass: approxi mate to 8 . 10(6) M.). It is seen in the (CO)-C-12(J = 1 --> 0), (CO)-C-12( J = 2 --> 1), (CO)-C-13(J = 1 --> 0) and (CO)-O-18(J = 1 --> 0) lines. The superbubble is centred around the most powerful su pernova 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 su ggest that hot coronal gas originating from inside the shell is the main co ntributor to the diffuse X-ray outflow in M 82. We briefly discuss observat ions of the same region at other wavelengths (radio continuum, optical, HI, X-rays, ionized gas). From our spectral line observations, we derive a kin ematic age of about 106 years for the superbubble. Using simple theoretical models, the total energy needed for the creation of this superbubble is of order 2 x 10(54) ergs. The required energy input rate (0.001 SN yr(-1)) is reasonable given the high supernova (SN) rate of approximate to 0.1 SN yr( -1) in the central part of M 82. As much as 10% of the energy needed to cre ate the superbubble is still present in form of the kinetic energy of the e xpanding molecular shell. Of order 10% is conserved in the hot X-ray emitti ng gas emerging from the superbubble into the halo of M 82. This newly dete cted 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 physica l properties of these sources.