The role of cloud initial conditions in setting the IMF

David Guszejnov

Poster -- Molecular clouds and filaments

The stellar initial mass function (IMF) is observed to be near-universal in the Milky Way and neighboring galaxies. Recent observations of early-type galaxies can be interpreted to imply a "bottom-heavy" IMF, while others of ultra-faint dwarfs could imply a "top-heavy" IMF. This would impose powerful constraints on star formation models. We explore what sort of "cloud-scale" IMF models could possibly satisfy these constraints using simulated galaxies as proxies, as they can provide the detailed star formation history and properties of each progenitor star-forming cloud. We find that no IMF models currently in the literature – nor any model where the characteristic mass is an arbitrary power-law function of the above quantities – can reproduce the claimed IMF variation both in ellipticals or dwarfs without severely violating observational constraints in the Milky Way (specifically, they predict too much variation in the “extreme” environments of the Galaxy, compared to that observed). Either the IMF varies in a much more complicated manner, or alternative interpretations of the extragalactic observations must be explored.