Optical Spectroscopy Of Metal-Rich Extragalactic Hii Regions

Fabio Bresolin
IfA

I discuss the properties of the stellar ionizing clusters 
of metal-rich (supersolar) extragalactic HII regions, as derived from 
ground-based spectroscopy in the optical. The sample studied includes a 
number of circumnuclear HII regions (hot spots), which are found in general 
to have spectral properties similar to the HII regions located in the
disks. 

I derive some conclusions on the age of the ionizing clusters and the shape 
of their upper initial stellar mass function by means of diagnostics of the 
stellar content (Wolf-Rayet star features, Balmer lines, He I lines), after a 
comparison with the predictions of current population synthesis evolutionary 
models. 

From a comparison with published photoionization models
based on synthetic cluster spectral energy distributions we find some
evidence for an overestimate of the number of He ionizing photons in
the model fluxes. In general, however, the massive star diagnostics
are in agreement with the predictions of recent evolutionary models 
calculated with a Salpeter initial mass function and a high upper mass limit. 
There is no compelling evidence for a depletion of massive stars (M > 40-50 
solar masses) in the initial mass function of metal-rich young clusters