Young Massive Stellar Clusters in the Milky Way: the Cl1813-178 and GLIMPSE 9 Clusters

Most of the stars, if not all, form in clusters, and clusters are generally found in large complexes. However, only a few of such complexes produce young massive clusters. We present first result of an ongoing study to fully map in time and space stellar clusters in two Galactic giant molecular clouds with the aim of understanding how star formation proceeded in the cloud, and of identifying the triggering mechanism. The W33 and GAL23.3-0.3 complexes are both located in the inner Galaxy, and are rich of HII regions, supernova remnants, and candidate clusters. The W33 complex contains one of the most massive Galactic stellar cluster with a mass of (104) M ⊙, and an age of 4.5 Myrs. The cluster location at the edge of the molecular complex suggests that this is a secondary episod of star formation. The GAL23.3-0.3 appears to contain much older massive stars (∼15 Myr).