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Herschel Observations of EXtra-Ordinary Sources: H_2S as a Probe of Dense Gas and Possibly Hidden Luminosity Toward the Orion KL Hot Core

Crockett, N. R. and Bergin, E. A. and Neill, J. L. and Black, J. H. and Blake, G. A. and Kleshcheva, M. (2014) Herschel Observations of EXtra-Ordinary Sources: H_2S as a Probe of Dense Gas and Possibly Hidden Luminosity Toward the Orion KL Hot Core. Astrophysical Journal, 781 (2). Art. No. 114. ISSN 0004-637X.

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We present Herschel/HIFI observations of the light hydride H_2S obtained from the full spectral scan of the Orion Kleinmann-Low nebula (Orion KL) taken as part of the Herschel Observations of EXtra-Ordinary Sources GT (guaranteed time) key program. In total, we observe 52, 24, and 8 unblended or slightly blended features from H_2^(32)S, H_2^(34)S, and H_2^(33)S, respectively. We only analyze emission from the so-called hot core, but emission from the plateau, extended ridge, and/or compact ridge are also detected. Rotation diagrams for ortho and para H_2S follow straight lines given the uncertainties and yield T_(rot) = 141 ± 12 K. This indicates H_2S is in local thermodynamic equilibrium and is well characterized by a single kinetic temperature or an intense far-IR radiation field is redistributing the population to produce the observed trend. We argue the latter scenario is more probable and find that the most highly excited states (E_(up) ≳ 1000 K) are likely populated primarily by radiation pumping. We derive a column density, N_(tot)(H_2^(32)S) = 9.5 ± 1.9 × 10^(17) cm^(–2), gas kinetic temperature, T_(kin) = 120±^(13)_(10) K, and constrain the H_2 volume density, n_H_2 ≳ 9 × 10^7 cm^(–3), for the H_2S emitting gas. These results point to an H_2S origin in markedly dense, heavily embedded gas, possibly in close proximity to a hidden self-luminous source (or sources), which are conceivably responsible for Orion KL's high luminosity. We also derive an H_2S ortho/para ratio of 1.7 ± 0.8 and set an upper limit for HDS/H_2S of <4.9 × 10^(–3).

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Crockett, N. R.0000-0002-6586-7591
Blake, G. A.0000-0003-0787-1610
Additional Information:© 2014 American Astronomical Society. Received 2013 July 18; accepted 2013 December 18; published 2014 January 15. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. We thank the anonymous referee who provided comments that improved this manuscript. 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 United States. Consortium members are Canada: CSA, University of 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 Astronόmico Nacional (IGN), Centro de Astrobiología (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. HIPE is a joint development by the Herschel Science Ground Segment Consortium, consisting of ESA, the NASA Herschel Science Center, and the HIFI, PACS, and SPIRE consortia. Support for this work was provided by NASA through an award issued by JPL/Caltech.
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Subject Keywords: ISM: abundances; ISM: individual objects (Orion KL); ISM: molecules
Issue or Number:2
Record Number:CaltechAUTHORS:20140321-102125739
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Official Citation:Herschel Observations of EXtra-Ordinary Sources: H2S as a Probe of Dense Gas and Possibly Hidden Luminosity Toward the Orion KL Hot Core N. R. Crockett et al. 2014 ApJ 781 114
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44444
Deposited By: Ruth Sustaita
Deposited On:21 Mar 2014 18:01
Last Modified:03 Oct 2019 06:18

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