The Young Star Clusters in blue compact galaxies: Evidence for a NIR excess and starburst properties

by Dr Angela Adamo (Astronomi)

Wednesday 27 Oct 2010, 10:30 → 11:30 Europe/Stockholm

FD51

Blue compact galaxies (BCGs) are very active star forming systems, characterized by bright UV and blue luminosities and low metallicity content. High-resolution data have revealed that the luminous star forming knots in these galaxies are formed by hundreds of young star clusters. We present here the first systematic study of the star cluster populations in 3 BCGs (Haro 11, ESO 185, and MRK 930) with major implication for the formation history of their host systems. The three galaxies show recent increased star formation rates and a high fraction of massive clusters, probably as a result of minor/major merger events. The age distributions have a peak of cluster formation only 3.5 Myr old, unveiling a unique sample of clusters still partially embedded. A considerable fraction of clusters (30-50 %) mainly younger than 10 Myr shows an observed flux excess between 0.8 and 2.2 micron. This so-called NIR excess is impossible to explain with evolutionary models including both stellar continuum and self-consistent treatment of the photoionized gas. We discuss possible explanations for this NIR excess addressing IR studies of both extragalactic young star clusters and resolved massive star forming regions in the Milky Way and in the nearby Magellanic Clouds.