Supersonic Line Broadening within Young and Massive Super Star Clusters
  The origin of supersonic infrared and radio recombination nebular lines often
detected in young and massive superstar clusters are discussed. We suggest that
these arise from a collection of repressurizing shocks (RSs), acting
effectively to re-establish pressure balance within the cluster volume and from
the cluster wind which leads to an even broader although much weaker component.
The supersonic lines are here shown to occur in clusters that undergo a bimodal
hydrodynamic solution (Tenorio-Tagle et al. 2007), that is within clusters that
are above the threshold line in the mechanical luminosity or cluster mass vs
the size of the cluster (Silich et al. 2004). The plethora of repressurizing
shocks is due to frequent and recurrent thermal instabilities that take place
within the matter reinserted by stellar winds and supernovae. We show that the
maximum speed of the RSs and of the cluster wind, are both functions of the
temperature reached at the stagnation radius. This temperature depends only on
the cluster heating efficiency ($\eta$). Based on our two dimensional
simulations (Wunsch et al. 2008) we calculate the line profiles that result
from several models and confirm our analytical predictions. From a comparison
between the predicted and observed values of the half-width zero intensity of
the two line components we conclude that the thermalization efficiency in SSC's
above the threshold line must be lower than 20%.
