Evidence for a Turnover in the Initial Mass Function of Low-mass Stars and Substellar Objects: Analysis from an Ensemble of Young Clusters

We present a combined analysis of the low-mass initial mass function (IMF) for seven star-forming regions. We first demonstrate that the ratios of stars to brown dwarfs are consistent with a single underlying IMF. By assuming that the underlying IMF is the same for all seven clusters and by combining the ratio of stars to brown dwarfs from each cluster, we constrain the shape of the brown dwarf IMF and find it to be consistent with a lognormal IMF. This provides the strongest constraint yet that the substellar IMF turns over ( , a dN/dM ∝ M ). a ! 0 Subject headings: stars: formation — stars: low-mass, brown dwarfs — stars: luminosity function, mass function — stars: pre–main-sequence