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Spitzer and JCMT observations of the active galactic nucleus in the Sombrero Galaxy (NGC 4594)

Bendo, George J. and Buckalew, Brent A. and Dale, Daniel A. and Draine, Bruce T. and Joseph, Robert D. and Kennicutt, Robert C., Jr. and Sheth, Kartik and Smith, John-David T. and Walter, Fabian and Calzetti, Daniela and Cannon, John M. and Engelbracht, Charles W. and Gordon, Karl D. and Helou, George and Hollenbach, David and Murphy, Eric J. and Roussel, Hélène (2006) Spitzer and JCMT observations of the active galactic nucleus in the Sombrero Galaxy (NGC 4594). Astrophysical Journal, 645 (1). pp. 134-147. ISSN 0004-637X.

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We present Spitzer 3.6–160 μm images, Spitzer mid-infrared spectra, and JCMT SCUBA 850 μm images of the Sombrero Galaxy (NGC 4594), an Sa galaxy with a 10^9 M⊙ ; low-luminosity active galactic nucleus (AGN). The brightest infrared sources in the galaxy are the nucleus and the dust ring. The spectral energy distribution of the AGN demonstrates that, while the environment around the AGN is a prominent source of mid-infrared emission, it is a relatively weak source of far-infrared emission, as had been inferred for AGNs in previous research. The weak nuclear 160 μm emission and the negligible polycyclic aromatic hydrocarbon emission from the nucleus also implies that the nucleus is a site of only weak star formation activity and the nucleus contains relatively little cool interstellar gas needed to fuel such activity. We propose that this galaxy may be representative of a subset of low-ionization nuclear emission region galaxies that are in a quiescent AGN phase because of the lack of gas needed to fuel circumnuclear star formation and Seyfert-like AGN activity. Surprisingly, the AGN is the predominant source of 850 μm emission. We examine the possible emission mechanisms that could give rise to the 850 μm emission and find that neither thermal dust emission, CO line emission, bremsstrahlung emission, nor the synchrotron emission observed at radio wavelengths can adequately explain the measured 850 μm flux density by themselves. The remaining possibilities for the source of the 850 μm emission include a combination of known emission mechanisms, synchrotron emission that is self-absorbed at wavelengths longer than 850 μm, or unidentified spectral lines in the 850 μm band.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Dale, Daniel A.0000-0002-5782-9093
Draine, Bruce T.0000-0002-0846-936X
Kennicutt, Robert C., Jr.0000-0001-5448-1821
Sheth, Kartik0000-0002-5496-4118
Smith, John-David T.0000-0003-1545-5078
Walter, Fabian0000-0003-4793-7880
Calzetti, Daniela0000-0002-5189-8004
Helou, George0000-0003-3367-3415
Murphy, Eric J.0000-0001-7089-7325
Additional Information:© 2006 The American Astronomical Society. Received 2006 January 5; accepted 2006 March 7. Support for this work, part of the Spitzer Space Telescope Legacy Science Program, was provided by NASA through contract 1224769, issued by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. B.T.D. was supported in part by NSF grant AST 04-06833.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
NSFAST 04-06833
Subject Keywords:galaxies: active— galaxies: individual (NGC 4594)— galaxies: ISM—galaxies: nuclei—infrared: galaxies
Issue or Number:1
Record Number:CaltechAUTHORS:BENapj06a
Persistent URL:
Official Citation:George J. Bendo et al 2006 ApJ 645 134
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7751
Deposited By: Lindsay Cleary
Deposited On:30 Jul 2007
Last Modified:09 Mar 2020 13:18

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