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Astron. Astrophys. 358, 514-520 (2000)
7. Conclusions
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 LFs inside and outside the solar circle are different at 96%
confidence level. The LF within the solar circle, built with 413
sources, peaks at , while the LF
outside the solar circle, built with 142 sources, peaks at
.
-
The IMF index we obtain is and
constant with galactocentric radius. At 50% cumulative probability for
the goodness of fit, and keeping
fixed at the best fit value, in the
inner Galaxy, and in the outer
Galaxy.
-
A power law distribution for the number of stars per MSFR has an
exponent in the inner Galaxy. But
in the outer Galaxy the best fit model corresponds to
. Thus, the expectation value for
the number of stars per MSFR with
decreases from 225 for to 120 for
.
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
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