Multi-seeded multi-mode formation of embedded clusters in the RMC: Structured star formation toward the south-east boundary

Abstract

The Rosette Molecular Complex contains embedded clusters with diverse properties and origins. We have previously explored the shell mode of formation in the north (Regions A & B) and the massive concentrations in the ridge (Region C). Here, we explore star formation towards the south of the complex, Region D, based on data from the spatially complete 2 Micron All Sky Survey. We find that stars are forming prolifically throughout this region in a highly structured mode with both clusters and loose aggregates detected. The most prominent cluster (Region D1) lies in the north-center. This cluster is over 20 pc to the south of the Monoceros ridge, the interface of the emerging young OB cluster NGC 2244 with its ambient molecular clouds. In addition, there are several branches stemming from AFGL 961 in Region C and extending to the south-east boundary of the cloud. We invoke a tree model to interpret this pattern, corresponding to probable tracks of abrupt turbulent excitation and subsequent decay. Alternatively, we discuss gravoturbulent collapse scenarios based on numerical simulations. Relative stellar ages and gas flow directions will differentiate between these mechanisms.