Abstract
The question whether or not the initial mass function (IMF) is universal, i.e. the same in all kinds of environments, is subject to intense debate. A number of recent observations have been interpreted as evidence for a nonstandard IMF. Hydrodynamical simulations indicate that the kinetic temperature of the collapsing molecular gas is crucial for the shape of the resulting IMF. Unfortunately, the kinetic temperature of the molecular gas in external galaxies is often not well constrained. We demonstrate the diagnostic power of a selected set of para-formaldehyde lines as tracers of the kinetic temperature as well as the gas density in external galaxies using our non-LTE radiative transfer model. With this new observational tool, we have engaged in characterizing the properties of the dense molecular gas phase in a number of nearby starburst galaxies and near AGN. Our first results suggest the existence of a dense molecular gas phase in these active environments that is significantly warmer than the dust and much warmer than dense molecular gas found in the disk of our own Galaxy.