An Origin for the Angular Momentum of Molecular Cloud Cores: a Prediction from Filament Fragmentation

The angular momentum of a molecular cloud core plays a key role in star formation, as it is directly related to the outflow and the jet emanating from the newborn star, and it eventually results in the formation of the protoplanetary disk. However, the origin of the core rotation and its time evolution are not well understood. Recent observations reveal that molecular clouds exhibit a ubiquity of filamentary structures and that star-forming cores are associated with the densest filaments. As these results suggest that dense cores form primarily in filaments, the mechanism of core formation from filament fragmentation should explain the distribution of the angular momentum of these cores. In this paper we analyze the relation between velocity fluctuations along the filament close to equilibrium, and the angular momentum of the cores formed along its crest. We first find that an isotropic velocity fluctuation that follows the three-dimensional Kolmogorov spectrum does not reproduce the observed angular momentum of molecular cloud cores. We then identify the need for a large power at small scales and study the effect of three power spectrum models. We show that the one-dimensional Kolmogorov power spectrum with a slope of -5/3 and an anisotropic model with reasonable parameters are compatible with the observations. Our results stress the importance of more detailed and systematic observations of both the velocity structure along filaments, and the angular momentum distribution of molecular cloud cores, to determine the validity of the mechanism of core formation from filamentary molecular clouds.