Star clusters in nearby star-forming galaxies as tracers of galaxy evolution

by Dr Angela Adamo (Astronomi)

Friday 14 Feb 2014, 10:30 → 11:30 Europe/Stockholm

FA31

Massive young star clusters (YSCs) are commonly formed in local galaxies and as such, they could be used as tracers of their galactic star formation histories, under the condition that we understand their formation and disruption mode. During my talk, I will mainly address two main topics, the origin of the near-IR excess, and the role of the galactic environment in shaping the cluster formation rate and disruption.  A recent multiband analysis (from far-UV to near-IR wavelengths) of the YSCs in Haro 11 has revealed an observed flux excess in the near-IR, impossible to reconcile with single stellar pop (SSP) models. This excess challenges both our understanding of cluster formation and the reliability of near-IR cluster studies, i.e. the only wavelength window accessible with the next generation of facilities (i.e. JWST). I will discuss the preliminary results achieved with SINFONI adaptive optic integral field spectroscopy and some tentative reconciliation between the observed data and the models. In the second part, I will focus on the role of the galactic environment in determining the fraction of stars forming in bound clusters and which fraction of clusters survives with time. There is increasing evidence that the fraction of star formation appending in bound YSCs (i.e. cluster formation efficiency, CFE) depends on the physical conditions of the galactic environment. If cluster formation would only be dominated by size-of-sample effect, one would expect the CFE to be constant (the number of clusters increase as function of increasing star formation rate but overall the fraction of star formation happening in star clusters is the same). At the same time, if clusters are disrupted in spite of their physical properties or the type of environment where they live, one would expect to not see any trend in their disruption rate. I will present the results achieved with the study of the cluster populations in a grand-design nearby spiral galaxy, M 83. The CFE and cluster disruption has been derived for the whole system as well as in different regions of the same galaxy. Overall, these results suggest that the CFE increases as function of star formation rate densities. Similarly disruption seams to decrease in the outer regions where the interstellar medium is less dens and shear is less strong.