Program: GN-2021A-Q-408

We discovered a giant shell of diffuse Halpha emission in the field of the M81/M82 group, using the Dragonfly Line Mapper. This may be a direct detection of the circumgalactic medium around M82, the nearest (and prototypical) starburst galaxy. While the morphology of the shell is suggestive of an association with M82, we cannot exclude the possibility that it is a wisp of ionized gas in the Milky Way. Here we propose to use GMOS spectroscopy of the shell to verify its existence and to determine whether it is associated with M82 or the Milky Way. The observations can be done in any seeing.