Spitzer Reveals Hidden Quasar Nuclei in Some Powerful FR II Radio Galaxies

By P. Ogle, D. Whysong, R. Antonucci. 2006

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We present a Spitzer mid-infrared survey of 42 Fanaroff-Riley class II radio galaxies and quasars from the 3CRR catalog at redshift z < 1. All of the quasars and 45% ± 12% of the narrow-line radio galaxies have a mid-IR luminosity of νLν(15 μm) > 8 × 1043 ergs s-1, indicating strong thermal emission from hot dust in the active galactic nucleus. Our results demonstrate the power of Spitzer to unveil dust-obscured quasars. The ratio of "mid-IR luminous" narrow-line radio galaxies to quasars indicates a mean dust covering fraction of 0.56 ± 0.15, assuming relatively isotropic emission. We analyze Spitzer spectra of the 14 mid-IR luminous narrow-line radio galaxies thought to host hidden quasar nuclei. Dust temperatures of 210-660 K are estimated from single-temperature blackbody fits to the low- and high-frequency ends of the mid-IR bump. Most of the mid-IR luminous radio galaxies have a 9.7 μm silicate absorption trough with optical depth <0.2, attributed to dust in a molecular torus. Forbidden emission lines from high-ionization oxygen, neon, and sulfur indicate a source of far-UV photons in the hidden nucleus. However, we find that the other 55% ± 13% of narrow-line FR II radio galaxies are weak at 15 μm, contrary to single-population unification schemes. Most of these galaxies are also weak at 30 μm. Mid-IR weak radio galaxies may constitute a separate population of nonthermal, jet-dominated sources with low accretion power.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/d7c39e2474c75bc9519838c2ff87f207dd7e8aa6

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In Astronomy and Astrophysics

1. D. M. Alexander
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In Nuclear and High Energy Physics

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Citations in the corpus

• IDENTIFYING LUMINOUS ACTIVE GALACTIC NUCLEI IN DEEP SURVEYS: REVISED IRAC SELECTION CRITERIA (2012, background): “…Sections 7 and 9 and the 16 The z> 1 3CRR radio galaxies discussed here lie at higher redshifts and have higher radio luminosities (νLν (178 MHz, rest)> 1044 ergs s−1) than the intrinsically MIR-weak and LINER-like narrow-line radio galaxies of Ogle et al. (2006), which may lack a hot dust torus.”
• The active nuclei of z < 1.0 3CRR radio sources (2009, methodology): “In the IR, the 3CRR objects in this redshift range have been studied by Ogle et al. (2006) and Cleary et al. (2007).”
• Spitzer Observations of 3C Quasars and Radio Galaxies: Mid-Infrared Properties of Powerful Radio Sources (2006, background): “Only 15 mdata were available for the objects in the supplementary sample from Ogle et al. (2006).”
• General relativistic magnetohydrodynamic simulations of magnetically choked accretion flows around black holes (2012, background): “178Mhz observations by Ogle et al. (2006) are affected by a lack of simultaneity between optical and radio emission, and the systems they observe could be low-luminosity radiatively inefficient systems that lowers their jet efficiency requirements.”
• Hot and cold gas accretion and feedback in radio-loud active galaxies (2007, background): “LERGs in general show no evidence in the mid-IR for an obscuring torus, either at low or high luminosities (Whysong & Antonucci 2004; Ogle et al. 2006) and their optical nuclei are consistent with being dominated purely by jet-related emission (Chiaberge et al. 2002).”
• MID-INFRARED SPECTROSCOPY OF SUBMILLIMETER GALAXIES: EXTENDED STAR FORMATION IN MASSIVE HIGH-REDSHIFT GALAXIES (2009, background): “This feature may correspond to [Siv] narrow-line emission, which is commonly associated with hot starburst activity or the presence of an AGN (Spoon et al. 2002; Ogle et al. 2006).”
• EMU: Evolutionary Map of the Universe (2011, background): “They also lack the expected infrared emission from a dusty torus (see e.g. Whysong & Antonucci 2004; Ogle et al. 2006) and do not show accretion-related X-ray emission (Hardcastle et al. 2006; Evans et al. 2006).”
• Optical Spectroscopy and X-Ray Detections of a Sample of Quasars and Active Galactic Nuclei Selected in the Mid-Infrared from Two Spitzer Space Telescope Wide-Area Surveys (2006, background): “Mid-infrared selection of AGN is effective because dust heated by the AGN forms a “calorimeter”, whose luminosity is not as strongly affected by obscuration as that in most other wavelength bands (except the radio) (e.g. Spinoglio et al. 1995; Meisenheimer et al. 2001; Ogle et al. 2006).”