A SCUBA survey of bright-rimmed clouds

Abstract

Context. Bright-rimmed clouds (BRCs) are potential examples of triggered star formation regions, in which photoionisation driven shocks caused by the expansion of HII regions induce protostellar collapse within the clouds. Aims. The main purpose of the paper is to establish the level of star formation occuring within a known set of BRCs. A secondary aim is to determine the extent, if any, to which this star formation has been promulgated by the process of photoionisation triggering. Methods. A primary set of observations is presented obtained with submillimeter SCUBA observations and archival data from near-IR and mid- to far-IR have been explored for relevant observations and incorporated where appropriate. Results. SCUBA observations show a total of 47 dense cores within the heads of 44 observed BRCs drawn from a catalogue of IRAS sources embedded within HII regions, supportive of the scenario proposed by RDI models. The physical properties of these cores indicate star formation across the majority of our sample. This star formation appears to be predominately in the regime of intermediate to high mass and may indicate the formation of clusters. IR observations indicate the association of early star forming sources with our sample. A fundamental difference appears to exist between different morphological types of BRC, which may indicate a different evolutionary pathway toward star formation in the different types of BRC. Conclusions. Bright-rimmed clouds are found to harbour star formation in its early stages. Different evolutionary scenarios are found to exist for different morphological types of BRC. The morphology of a BRC is described as type ‘A’, moderately curved rims, type ‘B’, tightly curved rims, and ‘C’, cometary rims. ‘B’ and ‘C’ morphological types show a clear link between their associated star formation and the strength of the ionisation field within which they are embedded. An analysis of the mass function of potentially induced star-forming regions indicate that radiatively-driven implosion of molecular clouds may contribute significantly toward the intermediate to high-mass stellar mass function.