The Massive Star Clusters in the Dwarf Merger ESO 185-IG13: is the Red
  Excess Ubiquitous in Starbursts?
  We have investigated the starburst properties of the luminous blue compact
galaxy ESO 185-IG13. The galaxy has been imaged with the high resolution
cameras onboard to the Hubble Space Telescope. From the UV to the IR, the data
reveal a system shaped by hundreds of young star clusters, and fine structures,
like a tidal stream and a shell. The presence of numerous clusters and the
perturbed morphology indicate that the galaxy has been involved in a recent
merger event. Using previous simulations of shell formation in galaxy mergers
we constrain potential progenitors of ESO 185-IG13. The analysis of the star
cluster population is used to investigate the properties of the present
starburst and to date the final merger event, which has produced hundreds of
clusters younger than 100 Myr. We have found a peak of cluster formation only
3.5 Myr old. A large fraction of these clusters will not survive after 10-20
Myr, due to the "infant mortality" caused by gas expulsion. However, this
sample of clusters represents an unique chance to investigate the youngest
phases of cluster evolution. As already observed in the analog blue compact
galaxy Haro 11, a fraction of young clusters are affected by a flux excess at
wavelengths longer than 8000 \AA. Ages, masses, and extinctions of clusters
with this NIR excess are estimated from UV and optical data. We discuss
similarities and differences of the observed NIR excess in ESO 185-IG13
clusters with other cases in the literature. The cluster ages and masses are
used to distinguish among the potential causes of the excess. We observe, as in
Haro 11, that the use of the IR and the (commonly used) I band data results in
overestimates of age and mass in clusters affected by the NIR excess. This has
important implications for a number of related studies of star clusters.
