Abstract
Accepted 1999 May 27. Received 1999 April 23; in original form 1999 February 17 ABSTRA C T We present MERLIN and VLA observations at 1.4 and 5 GHz of the diffuse radio emission in the centre of M82. We detect a large expanding shell of ionized gas surrounding the brightest supernova remnant 41:95 1 57:5 with a diameter of ,100 pc and an expansion velocity of ,100 km s 21 . We observe a 50-pc-scale ‘blow-out’ from this region, in the form of a ‘cone’ of missing 5-GHz continuum emission, which appears to be an excellent example of a galactic chimney. On larger radio scales, we observe four chimney structures extending out to the north ,100‐200 pc along the minor axis. One of these features is almost certainly related to the 50-pc-scale blow-out from 41:95 1 57:5, although this is not the most prominent feature. The other features have also been traced to expulsion of material from the very centre by using an ‘unsharp masked’ image from 5-GHz VLA B-array observations, with the supernova remnant removed. We interpret these chimney features as the base of the superwind, which implies that the ejection of material into the halo does not occur smoothly over the starburst region. Instead, very localized venting of hot gas is clearly in evidence.
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