Cloud Structure and the Origins of the Stellar Initial Mass Function in Ρ-ophiuchus

This article explores the relationship between dense molecular cores and young, pre-main sequence stars within the active star-forming giant molecular cloud ρ Ophiuchus. Our analyses synthesize multiwavelength data, including dust extinction maps, dust emission at 1.2mm, mid-infrared images, and molecular line emission from several species. Following the investigation of various dense core identification algorithms including a new technique based on Bayesian statistics our final sample of dense cores is determined from a hybrid of techniques applied to the 1.2mm dust emission map. The spatial distribution of these cores, measured with the two-point correlation function, appears scale free over two orders of magnitude in separation, mimicking the spatial distribution of young stars in this range. The measured velocity dispersion of high volume density gas in a subset of cores implies that a vast majority are stable against gravitational collapse. The systematically smaller average column densities measured for the larger cores and evidence for substructure in the high resolution dust maps suggest that some of the larger cores may fragment into multiple star systems. Approximately 6 cores harbor multiple embedded sources and new mid-infrared sources are found within 8 cores previously thought to be “starless.” Additionally, nine 1.2mm sources identified as cores are marginally resolved or unresolved sources coincident with known young stars and are likely to be heavily contaminated by circumstellar disk emission. In light of these results and the known high multiplicity of young stars, we find it unlikely that cores identified through dust emission or extinction have a one-to-one mapping with the subsequent generation of stars arising from them. To understand the similarities between ensembles of dense cores and the stellar initial mass function will require in depth studies that consider the distribution of dust, molecular line emission, and deep near and mid-infrared imaging from nearby active regions such as ρ Ophiuchus. Subject headings: stars: formation — stars: pre-main sequence — ISM: individual (ρ-Ophiuchus) — ISM: structure — ISM: clouds