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Published October 2010 | Published
Journal Article Open

The origin of the [C II] emission in the S140 photon-dominated regions. New insights from HIFI

Abstract

Using Herschel's HIFI instrument, we observe [C II] along a cut through S140, as well as high-J transitions of CO and HCO^+ at two positions on the cut, corresponding to the externally irradiated ionization front and the embedded massive star-forming core IRS1. The HIFI data were combined with available ground-based observations and modeled using the KOSMA-τ model for photon-dominated regions (PDRs). We derive the physical conditions in S140 and in particular the origin of [C II] emission around IRS1. We identify three distinct regions of [C II] emission from the cut, one close to the embedded source IRS1, one associated with the ionization front, and one further into the cloud. The line emission can be understood in terms of a clumpy model of PDRs. At the position of IRS1, we identify at least two distinct components contributing to the [C II] emission, one of them a small, hot component, which can possibly be identified with the irradiated outflow walls. This is consistent with the [C II] peak at IRS1 coinciding with shocked H_2 emission at the edges of the outflow cavity. We note that previously available observations of IRS1 can be reproduced well by a single-component KOSMA-τ model. Thus, it is HIFI's unprecedented spatial and spectral resolution, as well as its sensitivity that has allowed us to uncover an additional hot gas component in the S140 region.

Additional Information

© 2010 ESO. Received 31 May 2010, Accepted 28 July 2010, Published online 01 October 2010. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Acknowledgements and appendices (pages 5 to 7) are only available in electronic form at http://www.aanda.org. HIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada and the United States under the leadership of SRON Netherlands Institute for Space Research, Groningen, The Netherlands and with major contributions from Germany, France and the US. Consortium members are: Canada: CSA, U. Waterloo; France: CESR, LAB, LERMA, IRAM; Germany: KOSMA, MPIfR, MPS; Ireland, NUI Maynooth; Italy: ASI, IFSI-INAF, Osservatorio Astrofisico di Arcetri- INAF; Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observatorio Astronomico Nacional (IGN), Centro de Astrobiologia (CSIC-INTA). Sweden: Chalmers University of Technology – MC2, RSS & GARD; Onsala Space Observatory; Swedish National Space Board, Stockholm University – Stockholm Observatory; Switzerland: ETH Zurich, FHNW; USA: Caltech, JPL, NHSC. The work on star formation at ETH Zurich is partially funded by the Swiss National Science Foundation (grant nr. 200020-113556). This program is made possible thanks to the Swiss HIFI guaranteed time program. This work was supported by the German Deutsche Forschungsgemeinschaft, DFG project number Os 177/1–1. We thank the members of the Herschel key project "Galactic Cold Cores: A Herschel survey of the source populations revealed by Planck" lead by M. Juvela (KPOT_mjuvela_1) for providing us with the results of the SPIRE 250 μm mapping and fruitful discussions. We would also like to acknowledge the use of the JCMT CO(3–2) archival data (PI M. Thompson, M08BU15). A portion of this research was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space administration. We would like to thank an anonymous referee for constructive comments.

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