Chimneys in the starburst galaxy M82

We present MERLIN and VLA observations at 1.4 and 5 GHz of the diffuse radi o emission in the centre of M82. We detect a large expanding shell of ioniz ed gas surrounding the brightest supernova remnant 41.95 + 57.5 with a diam eter of similar to 100 pc and an expansion velocity of similar to 100 km s( -1). 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 excelle nt example of a galactic chimney. On larger radio scales, we observe four chimney structures extending out to the north similar to 100-200 pc along the minor axis. One of these feature s is almost certainly related to the 50-pc-scale blow-out from 41.95 + 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 supern ova remnant removed. We interpret these chimney features as the base of the superwind, which imp lies that the ejection of material into the halo does not occur smoothly ov er the starburst region. Instead, very localized venting of hot gas is clea rly in evidence.