Super star clusters in Haro 11: Properties of a very young starburst and
  evidence for a near-infrared flux excess
  We have used multi-band imaging to investigate the nature of the extreme
starburst environment in Haro 11 galaxy. The central starburst region has been
observed in 8 HST wavebands and at 2.16 micron at the ESO-VLT. We constructed
integrated spectral energy distributions (SEDs) for about 200 star clusters and
compared them with single stellar population models in order to derive ages,
masses and extinctions of thestar clusters. The present starburst has lasted
for 40 Myr, and shows a peak of cluster formation only 3.5 Myr old. With such
an extremely young cluster population, Haro 11 represents a unique opportunity
to investigate the youngest phase of the cluster formation process and
evolution in starburst systems. Extinction tends to diminish as function of the
cluster age, but the spread is large and for clusters in partial embedded
phases (< 5 Myr). A fraction of low-mass (> 10^4 Msun), very young (1-3 Myr)
clusters is missing, either because they are embedded inthe parental molecular
cloud and heavily extinguished, or because of blending. Almost half of the
cluster sample is affected by flux excesses at wavelengths 8000 \AA which
cannot be explained by simple stellar evolutionary models. Fitting SED models
over all wavebands leads to systematic overestimates of cluster ages and
incorrect masses for the stellar population supplying the light in these
clusters. We show that the red excess affects also the HST F814W filter, which
is typically used to constrain cluster physical properties. The clusters which
show the red excess are younger than 40 Myr; we propose possible physical
explanations for the phenomenon. Finally, we estimate that Haro 11 hasproduced
bound clusters at a rate almost a factor of 10 higher than the massive and
regular spirals, like the Milky Way. (Abriged)
