The Distribution of Dense Cores near H ii Regions

Abstract

An investigation of dust emission associated with a large sample of H ii regions has been carried out. Stacked results from this sample suggest that each H ii region is at or near the center of a cluster of dense cores that extends far beyond the H ii region, and has a volume density that decreases as r −3 . The data also show evidence for enhanced numbers of cores near the boundary of the H ii regions. At the same time, a significant decrease in the number of cores, consistent with no cores, is observed in the interior of these H ii regions. Neither these H ii regions nor their associated massive OB stars were found to have a significant heating effect on their associated dusty clumps. “Clouds,” or the outermost layers of the clumps in which the cores are embedded, are found to exert a strong shielding effect against external heating sources. Despite this, a large portion of the identified cores were found to be warmer than their surrounding clouds and consequently may be in the initial stages of star formation. The star-formation efficiency of the 7 H ii region systems with the most reliable mass budgets ranged between 1% and 9%.