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Herschel Observations of Extraordinary Sources: Analysis of the Full Herschel/HIFI Molecular Line Survey of Sagittarius B2(N)

Neill, Justin L. and Bergin, Edwin A. and Lis, Dariusz C. and Schilke, Peter and Crockett, Nathan R. and Favre, Cécile and Emprechtinger, Martin and Comito, Claudia and Qin, Sheng-Li and Anderson, Dana E. and Burkhardt, Andrew M. and Chen, Jo-Hsin and Harris, Brent J. and Lord, Steven D. and McGuire, Brett A. and McNeill, Trevor D. and Monje, Raquel R. and Phillips, Thomas G. and Steber, Amanda L. and Vasyunina, Tatiana and Yu, Shanshan (2014) Herschel Observations of Extraordinary Sources: Analysis of the Full Herschel/HIFI Molecular Line Survey of Sagittarius B2(N). Astrophysical Journal, 789 (1). Art. No. 8. ISSN 0004-637X. doi:10.1088/0004-637X/789/1/8.

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A sensitive broadband molecular line survey of the Sagittarius B2(N) star-forming region has been obtained with the Heterodyne Instrument for the Far-Infrared (HIFI) instrument on the Herschel Space Observatory, offering the first high spectral resolution look at this well-studied source in a wavelength region largely inaccessible from the ground (625–157 μm). From the roughly 8000 spectral features in the survey, a total of 72 isotopologues arising from 44 different molecules have been identified, ranging from light hydrides to complex organics, and arising from a variety of environments from cold and diffuse to hot and dense gas. We present a local thermodynamic equilibrium (LTE) model to the spectral signatures of each molecule, constraining the source sizes for hot core species with complementary Submillimeter Array interferometric observations and assuming that molecules with related functional group composition are cospatial. For each molecule, a single model is given to fit all of the emission and absorption features of that species across the entire 480–1910 GHz spectral range, accounting for multiple temperature and velocity components when needed to describe the spectrum. As with other HIFI surveys toward massive star-forming regions, methanol is found to contribute more integrated line intensity to the spectrum than any other species. We discuss the molecular abundances derived for the hot core where the LTE approximation is generally found to describe the spectrum well, in comparison to abundances derived for the same molecules in the Orion KL region from a similar HIFI survey. Notably, we find significantly higher abundances of amine- and amide-bearing molecules (CH_3NH_2, CH_2NH, and NH_2CHO) toward Sgr B2(N) than Orion KL and lower abundances of some complex oxygen-bearing molecules (CH_3OCHO in particular). In addition to information on the chemical composition of the hot core, the strong far-infrared dust continuum allows a number of molecules to be detected in absorption in the Sgr B2(N) envelope for the first time at high spectral resolution, and we discuss the possible physical origin of the kinematic components observed in absorption. Additionally, from the detection of new HOCO^+ transitions in absorption compared to published HCO^+ isotopic observations, we discuss constraints on the gas-phase CO_2 abundance and compare this to observations of the ice composition in the Galactic center region, and to CO_2 abundance estimates toward other high-mass star-forming regions. The reduced HIFI spectral scan and LTE model are made available to the public as a resource for future investigations of star-forming regions in the submillimeter and far-infrared.

Item Type:Article
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URLURL TypeDescription Paper
Bergin, Edwin A.0000-0003-4179-6394
Lis, Dariusz C.0000-0002-0500-4700
Schilke, Peter0000-0003-2141-5689
Crockett, Nathan R.0000-0002-6586-7591
Favre, Cécile0000-0002-5789-6931
Anderson, Dana E.0000-0002-8310-0554
Burkhardt, Andrew M.0000-0003-0799-0927
McGuire, Brett A.0000-0003-1254-4817
Additional Information:© 2014 The American Astronomical Society. Received 2013 August 30; Accepted 2014 April 28; Published 2014 June 9. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. 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 Astronómico Nacional (IGN), Centro de Astrobiología (CSIC-INTA); Sweden: Chalmers University of Technology–MC2, RSS and GARD, Onsala Space Observatory, Swedish National Space Board, Stockholm Observatory; Switzerland: ETH Zurich, FHNW; USA: Caltech, JPL, NHSC. Support for this work was provided by NASA through an award issued by JPL/Caltech. We thank Anthony Remijan and Joanna Corby for providing complementary data from other telescopes (GBT and BIMA) used in this manuscript.
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Subject Keywords:astrochemistry; ISM: clouds; ISM: individual objects (Sagittarius B2(N)); ISM: molecules
Issue or Number:1
Record Number:CaltechAUTHORS:20140728-100645147
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Official Citation:Herschel Observations of Extraordinary Sources: Analysis of the Full Herschel/HIFI Molecular Line Survey of Sagittarius B2(N) Justin L. Neill et al. 2014 ApJ 789 8
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:47520
Deposited By: Joanne McCole
Deposited On:28 Jul 2014 18:51
Last Modified:10 Nov 2021 17:40

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