We have constructed the FIR luminosity function for IRAS point sources with colours of UCH II regions and CS(2-1) detections, for different sectors in the galactic disk. The LFs are reliable above a luminosity of , and extend to in the high luminosity end, with a peak at . We analysed the trends in the LF of IRAS/CS sources in terms of an ensemble of massive star forming regions, and two free parameters suffice to provide a remarkably good fit to the shape of the LF. The fits required a maximum for the number of stars born in a given MSFR with . The best results were obtained setting for , and for . A few conclusions can be summarised:
The results of our analysis show that the observed luminosity functions for UCH II regions can be traced to the underlying young population. The differences within and outside the solar circle reflect a decrease in the average number of stars per massive star forming region towards the outer Galaxy, rather than a steeper IMF.
© European Southern Observatory (ESO) 2000
Online publication: June 8, 2000