Globules and pillars seen in the [CII] 158 μm line with SOFIA^⋆

¹ IRFU/SAp CEA/DSM, Laboratoire AIM CNRS – Université Paris Diderot, 91191 Gif-sur-Yvette, France
e-mail: nschneid@cea.fr
² Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ ESO, Karl Schwarzschild Str. 2, 85748 Garching, Germany
⁴ Boston College, Institute for Scientific Research, MA 02467, USA
⁵ KOSMA, I. Physik. Institut, Universität Köln, 50937 Köln, Germany
⁶ NOT, 38700 Santa Cruz de la Palma, Spain
⁷ SOFIA-USRA, NASA Ames Research Center, Moffett Field, CA 94035, USA
⁸ Astrophysikalisches Institut Potsdam, 14482 Potsdam, Germany
⁹ Deutsches SOFIA Institut, Universität Stuttgart, 70569 Stuttgart, Germany
¹⁰ Herschel Science Centre, ESAC, ESA, 28040 Madrid, Spain
¹¹ Univ. Bordeaux, LAB, UMR 5804, 33270 Floirac, France
¹² CNRS, LAB, UMR 5804, 33270 Floirac, France
¹³ National Optical Astronomy Observatory, Tucson, AZ 85719, USA
¹⁴ Dep. of Physics and Astronomy, U. of Toledo, OH 43606, USA
¹⁵ Dep. of Astronomy, U. of Massachusetts, Amherst MA, USA

Received: 30 January 2012
Accepted: 28 March 2012

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.