Abstract
We analyze the molecular interstellar medium around Westerlund 1, the most massive young stellar cluster known in the Milky Way. We have discovered an evacuated central region surrounded by two molecular complexes blue and red shifted with respect to the cluster. Our definition of the cloud is based on the gas kinematics and a model of Galactic spiral structure. These molecular regions are associated with ongoing star formation likely related to the presence of Westerlund 1.
