A Spitzer IRS Low-Resolution Spectroscopic Search for Buried AGNs in Nearby Ultraluminous Infrared Galaxies: A Constraint on Geometry between Energy Sources and Dust

By M. Imanishi, C. Dudley, R. Maiolino, P. Maloney, T. Nakagawa, G. R. N. Japan, Nrlgmu, Romé, U. Colorado, Isasjaxa and 1 more. 2007

142 citations recorded by the source corpus.

We present the results of Spitzer Infrared Spectrograph low-resolution infrared 5-35 μm spectroscopy of nearby ultraluminous infrared galaxies (ULIRGs) at z < 0.15. We focus on the search for the signatures of buried active galactic nuclei (AGNs) in the complete sample of ULIRGs classified optically as non-Seyferts (LINERs or H II regions). In addition to polycyclic aromatic hydrocarbon (PAH) emission features at 6.2, 7.7, and 11.3 μm, the conventional tool of starburst-AGN separation, we use the optical depths of the 9.7 and 18 μm silicate dust absorption features to infer the geometry of energy sources and dust at the nuclei of these ULIRGs, namely, whether the energy sources are spatially well mixed with dust (a normal starburst) or are more centrally concentrated than the dust (a buried AGN). Infrared spectra of at least 30%, and possibly 50%, of the observed optical non-Seyfert ULIRGs are naturally explained by emission consisting of (1) energetically insignificant, modestly obscured (AV < 20-30 mag) PAH-emitting normal starbursts and (2) energetically dominant, highly dust-obscured, centrally concentrated energy sources with no PAH emission. We interpret the latter component as a buried AGN. The fraction of ULIRGs showing some buried AGN signatures is higher in LINER ULIRGs than in H II region ULIRGs. Most of the luminous buried AGN candidates are found in ULIRGs with cool far-infrared colors. Where the absorption-corrected intrinsic AGN luminosities are derivable with little uncertainty, they are found to be of the order of 1012 L☉, accounting for the bulk of the ULIRGs' luminosities. The 5-35 μm spectroscopic starburst/AGN classifications are generally consistent with our previous classifications based on 3-4 μm spectra for the same sample.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/073da20673619ce65e9b0082db7ef0d80bd05a5d

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In Astronomy and Astrophysics

1. D. M. Alexander
2. Sylvain Veilleux
3. D. Rupke
4. H. Netzer
5. P. Hopkins
6. L. Hernquist
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In Instrumentation

1. Sylvain Veilleux
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3. D. Sanders
4. R. Genzel
5. L. Tacconi
6. D. Lutz
7. P. Hopkins
8. Lisa J. Kewley

Citations in the corpus

• THE ROLE OF STARBURST–ACTIVE GALACTIC NUCLEUS COMPOSITES IN LUMINOUS INFRARED GALAXY MERGERS: INSIGHTS FROM THE NEW OPTICAL CLASSIFICATION SCHEME (2009, background): “…wavelengths continue to be carried out to determine the energy source of ULIRGs (e.g., Tran et al. 2001; Farrah et al. 2003, 2007; Lı́pari et al. 2003; Ptak et al. 2003; Imanishi et al. 2007), determining the relative contribution of starbursts and AGN within individual galaxies is still difficult.”
• High-Resolution Mid-Infrared Spectroscopy of Ultraluminous Infrared Galaxies (2007, background): “…Tran et al. 2001), modeling of their 1Y1000 m spectral energy distributions (Klaas et al. 2001; Farrah et al. 2003), and X-ray observations (Franceschini et al. 2003; Ptak et al. 2003), although some recent studies suggest a significantly greater average AGN contribution (Imanishi et al. 2007).”
• A CHANDRA PERSPECTIVE ON GALAXY-WIDE X-RAY BINARY EMISSION AND ITS CORRELATION WITH STAR FORMATION RATE AND STELLAR MASS: NEW RESULTS FROM LUMINOUS INFRARED GALAXIES (2010, background): “…low-level AGN activity that affect estimates of the X-ray and/or infrared luminosities, two quantities that are important to this analysis (e.g., Imanishi et al. 2007, 2010; Iw09); (3) strong statistical fluctuations due to small numbers of luminous X-ray binaries that dominate the total X-ray…”
• SPITZER QUASAR AND ULIRG EVOLUTION STUDY (QUEST). IV. COMPARISON OF 1 Jy ULTRALUMINOUS INFRARED GALAXIES WITH PALOMAR-GREEN QUASARS (2009, background): “…(GTO and GO) programs have provided a wealth of new information on the physical properties of local ULIRGs (e.g., Armus et al. 2004, 2007; Farrah et al. 2007; Desai et al. 2007; Hao et al. 2007; Higdon et al. 2006; Imanishi et al. 2007; Lahuis et al. 2007; Spoon et al. 2007; CAo et al. 2008).”
• Radiative Feedback from Massive Black Holes in Elliptical Galaxies: AGN Flaring and Central Starburst Fueled by Recycled Gas (2007, background): “…outbursts, the emitting regions are so small ( 10 pc or less) that virtually the entire X-ray and IR luminosities would be seen as emitted by the central source; these phases also correspond to phases of high obscuration, with optical depth of the order of 100 (e.g., Imanishi et al. 2007).”