Ionisation impact of high-mass stars on interstellar filaments A Herschel study of the RCW36 bipolar nebula in Vela C

Abstract

Context. Ionising stars reshape their original molecular cloud and impact star formation, leading to spectacular morphologies such as bipolar nebulae around Hii regions. Molecular clouds are structured in filaments where stars principally form, as revealed by the Herschel space observatory. The prominent southern hemisphere Hii region, RCW36, is one of these bipolar nebulae. Aims. We study the physical connection between the filamentary structures of the Vela C molecular cloud and the bipolar morphology of RCW36, providing an in-depth view of the interplay occurring between ionisation and interstellar structures (bright-rims and pillars) around an Hii region. Methods. We have compared Herschel observations in five far-infrared and submillimetre filters with the PACS and SPIRE imagers, to dedicated numerical simulations and molecular line mapping. Results. Our results suggest that the RCW36 bipolar morphology is a natural evolution of its filamentary beginnings under the impact of ionisation. Conclusions. Such results demonstrate that, filamentary structures can be the location of very dynamical phenomena inducing the formation of dense clumps at the edge of Hii regions. Moreover, these results could apply to better understanding the bipolar nebulae as a consequence of the expansion of an Hii region within a molecular ridge or an interstellar filament.