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Detection of the Buried Active Galactic Nucleus in NGC 6240 with the Infrared Spectrograph on the Spitzer Space Telescope
The Astrophysical Journal (2006)
  • L. Armus, California Institute of Technology
  • J. Bernard-Salas, Cornell University
  • H.W.W. Spoon, Cornell University
  • J.A. Marshall, Cornell University
  • V. Charmandaris, University of Crete
  • Sarah J.U. Higdon, Cornell University
  • V. Desai, California Institute of Technology
  • L. Hao, Cornell University
  • H.I. Teplitz, California Institute of Technology
  • D. Devost, Cornell University
  • B.R. Brandl, Leiden University
  • B.T. Soifer, California Institute of Technology
  • J.R. Houck, Cornell University
We present mid-infrared spectra of the nearby ultraluminous infrared galaxy NGC 6240 taken with the Infrared Spectrograph ( IRS) on the Spitzer Space Telescope. The spectrum of NGC 6240 is dominated by strong fine-structure lines, rotational H2 lines, and polycyclic aromatic hydrocarbon (PAH) emission features. The H2 line fluxes suggest molecular gas at a variety of temperatures. A simple two-temperature fit to the S(0) through S(7) lines implies a mass of 6:7 ; 106 M at T  957 K and 1:6 ; 109 M at T 164 K, or about 15% of the total molecular gas mass in this system. Notably, we have detected the [Ne v] 14.3 m emission line, with a flux of 5 ; 1014 ergs cm2 s1, providing the first direct detection of the buried active galactic nucleus (AGN ) in the mid-infrared. Modeling of the total spectral energy distribution (SED) from near- to far-infrared wavelengths requires the presence of a hot dust (T  700 K) component, which we also associate with the buried AGN. The small [Ne v]/[Ne ii] and [Ne v]/IR flux ratios, the relative fraction of hot dust emission, and the large 6.2 m PAH equivalent width (EQW ), are all consistent with an apparent AGN contribution of only 3%–5% to the bolometric luminosity. However, correcting the measured [Ne v] flux by the extinction implied by the silicate optical depth and our SED fitting suggests an intrinsic fractional AGN contribution to the bolometric luminosity of 20%–24% in NGC 6240, which lies within the range implied by fits to the hard X-ray spectrum. Sub
  • Galaxies,
  • Active,
  • Individual,
  • Infrared
Publication Date
March 20, 2006
Publisher Statement
This version of the paper was obtained from In order for the work to be deposited in, the author must have copyright or it must be available under the Creative Commons Attribution license,Creative Commons Attribution-Noncommercial-ShareAlike license, orCreate Commons Public Domain Declaration. The publisher's final edited version of this article will be available at The Astrophysical Journal.
Citation Information
Sarah J.U. Higdon. "Detection of the Buried Active Galactic Nucleus in NGC 6240 with the Infrared Spectrograph on the Spitzer Space Telescope" The Astrophysical Journal Vol. 640 Iss. 1 (2006) p. 204 - 210
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