Globules and pillars seen in the [CII] 158 μ m line with SOFIA

Abstract

Molecular globules and pillars are spectacular features, found only in the interface region between a molecular cloud and an H II-region. Impacting far-ultraviolet (FUV) radiation creates photon-dominated regions (PDRs) on their surfaces that can be traced by typical cooling lines. With the GREAT receiver onboard SOFIA we mapped and spectrally resolved the [C II] 158 μm atomic fine-structure line and the highly excited 12CO J = 11 → 10 molecular line from three objects in Cygnus X (a pillar, a globule, and a strong IRAS source). We focus here on the globule and compare our data with existing Spitzer data and recent Herschel open-time PACS data. Extended [C II] emission and more compact CO-emission was found in the globule. We ascribe this emission mainly to an internal PDR, created by a possibly embedded star-cluster with at least one early B-star. However, external PDR emission caused by the excitation by the Cyg OB2 association cannot be fully excluded. The velocity-resolved [C II] emission traces the emission of PDR surfaces, possible rotation of the globule, and high-velocity outflowing gas. The globule shows a velocity shift of ∼2 km s -1 with respect to the expanding H II-region, which can be understood as the residual turbulence of the molecular cloud from which the globule arose. This scenario is compatible with recent numerical simulations that emphazise the effect of turbulence. It is remarkable that an isolated globule shows these strong dynamical features traced by the [C II]-line, but it demands more observational studies to verify if there is indeed an embedded cluster of B-stars. © 2012 ESO.