Abstract

We present new high-resolution optical spectroscopy of giant HII regions around three young massive clusters located in the blue dwarf galaxies NGC 5253 and He 2-10. We used the observations to derive the mass of the clusters under the hypothesis of virialization. The virial masses exceed the optical ones. In one case, however, the virial mass is consistent with that derived from the IR luminosity, pointing to the presence of a hidden stellar population. The dynamics inferred from the emission lines indicates that the clusters may indeed be virialized or close to virialization. We detect an indication of mass segregation in two clusters. At least in one case, we find that such mass segregation must have a "primordial" nature, rather than dynamical, i.e. associated with the formation mechanism of the cluster. We could resolve two of the clusters with the spectro-astrometric technique detecting in both cases evidence of structures on the pc scale. © ESO 2006.