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Herschel Far-infrared Spectroscopy of the Galactic Center. Hot Molecular Gas: Shocks versus Radiation near Sgr A*

Goicoechea, Javier R. and Etxaluze, M. and Cernicharo, J. and Gerin, M. and Neufeld, D. A. and Contursi, A. and Bell, T. A. and De Luca, M. and Encrenaz, P. and Indriolo, N. and Lis, D. C. and Polehampton, E. T. and Sonnentrucker, P. (2013) Herschel Far-infrared Spectroscopy of the Galactic Center. Hot Molecular Gas: Shocks versus Radiation near Sgr A*. Astrophysical Journal Letters, 769 (1). Art. No. L13. ISSN 2041-8205. https://resolver.caltech.edu/CaltechAUTHORS:20130719-150235405

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Abstract

We present a ~52-671 μm spectral scan toward Sgr A* taken with the PACS and SPIRE spectrometers on board Herschel. The achieved angular resolution allows us to separate, for the first time at far-IR wavelengths, the emission toward the central cavity (gas in the inner central parsec of the galaxy) from that of the surrounding circumnuclear disk. The spectrum toward Sgr A* is dominated by strong [O III], [O I], [C II], [N III], [N II], and [C I] fine-structure lines (in decreasing order of luminosity) arising in gas irradiated by UV photons from the central stellar cluster. In addition, rotationally excited lines of ^(12)CO (from J = 4-3 to 24-23), ^(13)CO, H_(2)O, OH, H_(3)O+, HCO+, and HCN, as well as ground-state absorption lines of OH+, H_(2)O+, H_(3)O+, CH+, H_(2)O, OH, HF, CH, and NH are detected. The excitation of the ^(12)CO ladder is consistent with a hot isothermal component at T_k ≃ 10^(3.1) K and n(H_2) ≲ 10^4 cm^(–3). It is also consistent with a distribution of temperature components at higher density with most CO at T k ≲ 300 K. The detected molecular features suggest that, at present, neither very enhanced X-ray nor cosmic-ray fluxes play a dominant role in the heating of the hot molecular gas. The hot CO component (either the bulk of the CO column or just a small fraction depending on the above scenario) results from a combination of UV- and shock-driven heating. If irradiated dense clumps/clouds do not exist, shocks likely dominate the heating of the hot molecular gas. This is consistent with the high-velocity gas detected toward Sgr A*.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1088/2041-8205/769/1/L13DOIArticle
http://iopscience.iop.org/2041-8205/769/1/L13PublisherArticle
http://arxiv.org/abs/1305.1119arXivDiscussion Paper
ORCID:
AuthorORCID
Neufeld, D. A.0000-0001-8341-1646
Indriolo, N.0000-0001-8533-6440
Lis, D. C.0000-0002-0500-4700
Additional Information:© 2013 American Astronomical Society. Received 2013 January 26; accepted 2013 March 28; published 2013 May 7. We thank C. Lang and M. A. Requena-Torres for providing us with the VLA 6 cm radiocontinuum image in CLASS format, and C. Joblin and O. Bernè for useful discussions on the Orion Bar. We thank the Spanish MINECO for funding support from grants AYA2009-07304, CSD2009-00038, and S2009ESP-1496, and NASA through an award issued by JPL/ Caltech. J.R.G. is supported by a Ramón y Cajal research contract. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Funders:
Funding AgencyGrant Number
Ministerio de Economía, Industria y Competitividad (MINECO)AYA2009-07304
Ministerio de Economía, Industria y Competitividad (MINECO)CSD2009-00038
Ministerio de Economía, Industria y Competitividad (MINECO)S2009ESP-1496
NASA/JPL/CaltechUNSPECIFIED
Ramón y Cajal ProgrammeUNSPECIFIED
Subject Keywords:black hole physics; Galaxy: center; infrared: ISM; ISM: molecules; shock waves
Issue or Number:1
Record Number:CaltechAUTHORS:20130719-150235405
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20130719-150235405
Official Citation:Herschel* Far-infrared Spectroscopy of the Galactic Center. Hot Molecular Gas: Shocks versus Radiation near Sgr A Javier R. Goicoechea et al. 2013 ApJ 769 L13
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39474
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:22 Jul 2013 23:23
Last Modified:09 Mar 2020 13:19

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