1999MNRAS.309..395W

We present MERLIN and VLA observations at 1.4 and 5GHz 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+57.5 with a diameter of ∼100pc and an expansion velocity of ∼100km.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 excellent example of a galactic chimney.

On larger radio scales, we observe four chimney structures extending out to the north ∼100-200pc along the minor axis. One of these features 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 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.