A study of the luminosity and mass functions of very young stellar clusters

We now know that the star formation process results in freely-floating objects with masses spanning nearly four orders of magnitude. However, both the distribution of these objects' masses at birth and the precise physics responsible for the shape of this initial mass function are poorly known and can be improved upon by focusing on very young star clusters just emerging from their parental molecular clouds. In this dissertation I have investigated the usefulness of the observed luminosity function of a very young cluster as a tool for deriving that cluster's underlying mass function. I find that a cluster's luminosity function is an excellent probe of the initial mass function over the entire range of stellar and substellar mass and can be utilized to acquire the statistics necessary for testing the hypothesis of a universal mass function.; To study the luminosity and mass functions of such clusters I developed a Monte Carlo based population synthesis algorithm applicable to pre-main sequence stars. Using this algorithm I performed numerical experiments testing the sensitivity of model luminosity functions to changes in fundamental cluster parameters. After showing that the luminosity function is intrinsically most sensitive to the form of the underlying mass function, I studied three young clusters, NGC 2362, IC 348 and the Trapezium, and performed deep near-infrared surveys to construct their K-band luminosity functions. Using the model luminosity function algorithm, I derived each cluster's underlying mass function and found them to be remarkably similar, with all forming broad peaks at subsolar masses. Where these census are sufficiently deep I find that the mass function turns over and declines in number throughout the substellar regime but appears to contain structure near the deuterium-burning limit. Regardless, I find that brown dwarfs do not dominate stars either by number or total mass. Lastly, I use a statistically significant sample of candidate brown dwarfs to show that these objects appear as likely to have been born with circumstellar disks as stars. Combining this finding with the continuity of the shape of the initial mass function across numerous environments suggests that a single physical mechanism may dominate the star formation process.