How warm is the molecular gas in active environments?
  The question whether or not the initial mass function is universal, i.e. the
same in all kinds of environments, is of critical importance for the theory of
star formation and still intensely debated. A top-heavy initial mass function
may be the result of star formation out of dense molecular clouds with a
temperature of ~ 100 K. Such a molecular gas phase is not commonly found in the
Galactic plane, but may be present in active environments like cores of
starburst galaxies or AGN. Unfortunately, the kinetic temperature of the
molecular gas in external galaxies is often not well constrained. Having proven
the diagnostic power of selected formaldehyde lines as tracers of the
properties of the molecular gas in external galaxies, we have engaged in
observing these diagnostic lines in a number of starburst galaxies or near AGN.
This contribution presents the latest results of these studies.
