Very Low Luminosity Young Cluster and the Luminosity and Mass Functions in S106

We present the results of deep near- infrared observations searching for very lowmass young stellar objects ( YSOs) in the massive star- forming region of S106 taken with the Subaru Telescope. The survey, whose limiting magnitude exceeds 20 mag in the JHK' bands, is sensitive enough to provide unprecedented details in the two nebular lobes. In addition, it reveals a census of the stellar population down to objects below the deuterium- burning limit, a fiducial boundary between brown dwarfs and planetary- mass objects. Based on color- color diagrams, nearly 600 embedded YSO candidates with near- infrared excesses have been identified in an area of similar to 5' x 5' that are not uniformly distributed but centrally concentrated. Combining the reddening- corrected luminosity of the YSO candidates with the theoretical evolutionary models, we suggest that there exists a substantial substellar population. If we divide the cluster into three subgroups based on stellar and cloud properties, both their luminosity functions and mass functions across the stellar- substellar boundary demonstrate local variation on a subparsec scale. Nevertheless, all the mass functions have distinct characteristics in common: they do not have any turnover and do not decline down to the completeness limits. Furthermore, the mass function for S106 appears to be more abundant in young substellar objects compared to those obtained for other young clusters, such as Trapezium and IC 348. This implies that the substellar mass function for young clusters may have a variation.