Globules and pillars in Cygnus X

III. Herschel and upGREAT/SOFIA far-infrared spectroscopy of the globule IRAS 20319+3958 in Cygnus X^★

¹ I. Physik. Institut, University of Cologne, Zülpicher Str. 77, 50937 Cologne, Germany
e-mail: nschneid@ph1.uni-koeln.de
² RAL Space, STFC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK
³ ESO, Karl Schwarzschild Str. 2, 85748 Garching, Germany
⁴ Nordic Optical Telescope, Rambla José Ana Fernández Pérez 7, 38711 Breña Baja, Spain
⁵ Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
⁶ Department of Physics and Astronomy, West Virginia University, Morgantown, WV 26506, USA
⁷ Laboratoire d’Astrophysique de Bordeaux, Université de Bordeaux, CNRS, B18N, allée G. Saint-Hilaire, 33615 Pessac, France
⁸ Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁹ Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
¹⁰ SOFIA-USRA, NASA Ames Research Center, MS 232-12, Moffett Field, CA 94035, USA
¹¹ DLR, Rutherfordstraße 2, 12489 Berlin-Adlershof, Germany

Received: 17 March 2021
Accepted: 13 August 2021

Abstract

IRAS 20319+3958 in Cygnus X South is a rare example of a free-floating globule (mass ~240 M_⊙, length ~1.5 pc) with an internal H II region created by the stellar feedback of embedded intermediate-mass stars, in particular, one Herbig Be star. In Schneider et al. 2012, (A&A, 542, L18) and Djupvik et al. 2017, (A&A, 599, A37), we proposed that the emission of the far-infrared (FIR) lines of [C II] at 158 μm and [O I] at 145 μm in the globule head are mostly due to an internal photodissociation region (PDR). Here, we present a Herschel/HIFI [C II] 158 μm map of the whole globule and a large set of other FIR lines (mid-to high-J CO lines observed with Herschel/PACS and SPIRE, the [O I] 63 μm line and the ¹²CO 16→15 line observed with upGREAT on SOFIA), covering the globule head and partly a position in the tail. The [C II] map revealed that the whole globule is probably rotating. Highly collimated, high-velocity [C II] emission is detected close to the Herbig Be star. We performed a PDR analysis using the KOSMA-τ PDR code for one position in the head and one in the tail. The observed FIR lines in the head can be reproduced with a two-component model: an extended, non-clumpy outer PDR shell and a clumpy, dense, and thin inner PDR layer, representing the interface between the H II region cavity and the external PDR. The modelled internal UV field of ~2500 G_° is similar to what we obtained from the Herschel FIR fluxes, but lower than what we estimated from the census of the embedded stars. External illumination from the ~30 pc distant Cyg OB2 cluster, producing an UV field of ~150–600 G_° as an upper limit, is responsible for most of the [C II] emission. For the tail, we modelled the emission with a non-clumpy component, exposed to a UV-field of around 140 G_°.