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Herschel-PACS Observations of Far-IR CO Line Emission in NGC 1068: Highly Excited Molecular Gas in the Circumnuclear Disk

Hailey-Dunsheath, S. and Sturm, E. and Fischer, J. and Sternberg, A. and Graciá-Carpio, J. and Davies, R. and González-Alfonso, E. and Mark, D. and Poglitsch, A. and Contursi, A. and Genzel, R. and Lutz, D. and Tacconi, L. and Veilleux, S. and Verma, A. and de Jong, J. A. (2012) Herschel-PACS Observations of Far-IR CO Line Emission in NGC 1068: Highly Excited Molecular Gas in the Circumnuclear Disk. Astrophysical Journal, 755 (1). Art. No. 57. ISSN 0004-637X. doi:10.1088/0004-637X/755/1/57.

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We report the detection of far-IR CO rotational emission from the prototypical Seyfert 2 galaxy NGC 1068. Using Herschel-PACS, we have detected 11 transitions in the J_(upper) = 14-30 (E_(upper)/k_B = 580-2565 K) range, all of which are consistent with arising from within the central 10" (700 pc). The detected transitions are modeled as arising from two different components: a moderate-excitation (ME) component close to the galaxy systemic velocity and a high-excitation (HE) component that is blueshifted by ~80 km s^(–1). We employ a large velocity gradient model and derive n_(H2) ~ 10^(5.6) cm^(–3), T_(kin) ~ 170 K, and M_(H2) ~ 10^(6.7) M_☉ for the ME component and n_(H2) ~ 10^(6.4) cm^(–3), T_(kin) ~ 570 K, and M_(H2) ~ 10^(5.6) M_☉ for the HE component, although for both components the uncertainties in the density and mass are ±(0.6-0.9) dex. Both components arise from denser and possibly warmer gas than traced by low-J CO transitions, and the ME component likely makes a significant contribution to the mass budget in the nuclear region. We compare the CO line profiles with those of other molecular tracers observed at higher spatial and spectral resolution and find that the ME transitions are consistent with these lines arising in the ~200 pc diameter ring of material traced by H_2 1-0 S(1) observations. The blueshift of the HE lines may also be consistent with the bluest regions of this H_2 ring, but a better kinematic match is found with a clump of infalling gas ~40 pc north of the active galactic nucleus (AGN). We consider potential heating mechanisms and conclude that X-ray- or shock heating of both components is viable, while far-UV heating is unlikely. We discuss the prospects of placing the HE component near the AGN and conclude that while the moderate thermal pressure precludes an association with the ~1 pc radius H_2O maser disk, the HE component could potentially be located only a few parsecs more distant from the AGN and might then provide the N_H ~ 10^(25) cm^(–2) column obscuring the nuclear hard X-rays. Finally, we also report sensitive upper limits extending up to J_(upper) = 50, which place constraints on a previous model prediction for the CO emission from the X-ray obscuring torus.

Item Type:Article
Related URLs:
URLURL TypeDescription
Hailey-Dunsheath, S.0000-0002-8504-7988
Fischer, J.0000-0001-6697-7808
Genzel, R.0000-0002-2767-9653
Lutz, D.0000-0003-0291-9582
Tacconi, L.0000-0002-1485-9401
Veilleux, S.0000-0002-3158-6820
Additional Information:© 2012 American Astronomical Society. Received 2012 February 5; accepted 2012 June 6; published 2012 July 26. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. We thank Eva Schinnerer for generously providing her IRAM PdBI CO(1–0) and CO(2–1) data and Francisco Müller Sánchez for providing his SINFONI/VLT H2 1–0 S(1) map. We also thank an anonymous referee for many helpful comments on an early draft of this manuscript. Basic research in IR astronomy at NRL is funded by the US ONR; J.F. also acknowledges support from the NHSC. We thank the DFG for support via German-Israel Project Cooperation grant STE1869/1-1.GE625/15-1. E.G.-A. thanks the support by the Spanish Ministerio de Ciencia e Innovaciόn under project AYA2010-21697-C05-01 and is a Research Associate at the Harvard-Smithsonian Center for Astrophysics. S.V. acknowledges support from a Senior NPP Award from NASA and thanks the host institution, the Goddard Space Flight Center. PACS has been developed by a consortium of institutes led by MPE (Germany) and including UVIE (Austria); KU Leuven, CSL, IMEC (Belgium); CEA, LAM (France); MPIA (Germany); INAF-IFSI/OAA/OAP/ OAT, LENS, SISSA (Italy); IAC (Spain). This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/ CNES (France), DLR (Germany), ASI/ INAF (Italy), and CICYT/ MCYT (Spain).
Funding AgencyGrant Number
Office of Naval Research (ONR)UNSPECIFIED
German-Israeli Project CooperationSTE1869/1-1.GE625/15-1
Spanish Ministerio de Ciencia e InnovaciónAYA2010-21697-C05-01
Subject Keywords:galaxies: active; galaxies: individual (NGC 1068); galaxies: ISM; galaxies: nuclei; galaxies: Seyfert; infrared: galaxies
Issue or Number:1
Record Number:CaltechAUTHORS:20120905-085644068
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Official Citation:Herschel-PACS Observations of Far-IR CO Line Emission in NGC 1068: Highly Excited Molecular Gas in the Circumnuclear Disk S. Hailey-Dunsheath et al. 2012 ApJ 755 57
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33848
Deposited By: Ruth Sustaita
Deposited On:05 Sep 2012 16:41
Last Modified:09 Nov 2021 23:05

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