From the cradle to limbo: A Bayesian study of the substellar mass function

In this thesis, I explore the shape of the brown dwarf mass function and the role it plays in the exploration of star formation. In particular, I construct synthetic models of the brown dwarf luminosity function in three environments: young (10 Myr--1 Gyr) stellar clusters, the local Solar Neighborhood, and binary systems. These models are constructed from the Burrows et al. (2001) brown dwarf evolutionary models with hypothetical mass and age distributions. The synthetic luminosity functions are compared to the data via a Bayesian statistical approach.; Each environment yields unique discoveries. Analysis of young cluster luminosity functions finds an unexpected peak that fades with age. This peak is due to high mass brown dwarfs that burn deuterium and appears to be present in the nearby cluster IC 2391. Bayesian analysis of field brown dwarf space densities demonstrates that the mass function is continuous through the stellar/substellar boundary. This implies that formation continues smoothly from stars to brown dwarfs. Finally, study of the brown dwarf binary distribution demonstrates that the apparent predilection toward near-equal mass, tight systems is a real physical feature and not an observational bias. Two extensive surveys for wide companions to late-M and L dwarfs found no confirmed candidates. These two findings are consistent with, though not proof of, the cluster ejection scenario first espoused by Reipurth & Clarke (2001). The overall finding of this thesis is that the brown dwarf mass function is not well constrained by current observations. Future efforts to obtain better constraints are discussed. They include using new ground-based and space-based instruments to map young clusters and the field to deeper limits and new coronagraphic adaptive optics systems to probe smaller separation binary systems.