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Spitzer reveals hidden quasar nuclei in some powerful fr II radio galaxies

Ogle, Patrick and Whysong, David and Antonucci, Robert (2006) Spitzer reveals hidden quasar nuclei in some powerful fr II radio galaxies. Astrophysical Journal, 647 (1). pp. 161-171. ISSN 0004-637X. https://resolver.caltech.edu/CaltechAUTHORS:OGLapj06

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Abstract

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 vLv(15µm) > 8 × 10 to the 43rd 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 15µm, contrary to single-population unification schemes. Most of these galaxies are also weak at 30µm. Mid-IR weak radio galaxies may constitute a separate population of nonthermal, jet-dominated sources with low accretion power.


Item Type:Article
ORCID:
AuthorORCID
Ogle, Patrick0000-0002-3471-981X
Additional Information:© 2006 The American Astronomical Society. Received 2005 July 13; accepted 2006 April 19. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. We have also made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Support for this research was provided by NASA through an award issued by JPL/Caltech. We thank Dave Meier, Lee Armus, Bill Reach, and the anonymous referee for their helpful input and comments on the manuscript.
Funders:
Funding AgencyGrant Number
NASA1407
NASA/JPL/CaltechUNSPECIFIED
Subject Keywords:galaxies: active—galaxies: jets—infrared: galaxies—quasars: general
Issue or Number:1
Record Number:CaltechAUTHORS:OGLapj06
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:OGLapj06
Alternative URL:http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v647n1/63225/brief/63225.abstract.html
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7224
Collection:CaltechAUTHORS
Deposited By: Lindsay Cleary
Deposited On:23 Jan 2007
Last Modified:02 Oct 2019 23:40

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