Mid-infrared spectroscopy of high-redshift 3CRR sources

Abstract

Using the Spitzer Space Telescope, we have obtained rest frame 9-16mu spectra of 11 quasars and 9 radio galaxies from the 3CRR catalog at redshifts 1.0<z<1.4. This complete flux-limited 178MHz-selected sample is unbiased with respect to orientation and therefore suited to study orientation-dependent effects in the most powerful active galactic nuclei (AGN). The mean radio galaxy spectrum shows a clear silicate absorption feature (tau_9.7mu = 1.1) whereas the mean quasar spectrum shows silicates in emission. The mean radio galaxy spectrum matches a dust-absorbed mean quasar spectrum in both shape and overall flux level. The data for individual objects conform to these results. The trend of the silicate depth to increase with decreasing core fraction of the radio source further supports that for this sample, orientation is the main driver for the difference between radio galaxies and quasars, as predicted by AGN unification. However, comparing our high-z sample with lower redshift 3CRR objects reveals that the absorption of the high-z radio galaxy MIR continuum is lower than expected from a scaled up version of lower luminosity sources, and we discuss some effects that may explain these trends.

16 pages, 8 Figures, accepted for ApJ

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• Revealing the heavily obscured AGN population of High Redshift 3CRR Sources with Chandra X-ray Observations
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• Self-consistent 2-phase AGN torus models: SED library for observers
• Spitzer Mid-IR Spectroscopy of Powerful 2Jy and 3CRR Radio Galaxies. II. AGN Power Indicators and Unification
• The AGN-Star Formation Connection: Future Prospects with JWST
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• Quantifying the anisotropy in the infrared emission of powerful AGN
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• The Mid-infrared Emission of Narrow-Line Active Galactic Nuclei: Star-Formation, Nuclear Activity and two populations revealed by WISE
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• On the origin of the gamma-ray/optical lags in luminous blazars
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• Starbursts and dusty tori in distant 3CR radio galaxies
• Beyond Simple AGN Unification with Chandra-observed 3CRR Sources
• A panchromatic review of thermal and nonthermal active galactic nuclei
• Infrared colour properties of nearby radio-luminous galaxies
• Broad-band Jet Emission in Young and Powerful Radio Sources: the Case of the CSS Quasar 3C 186
• Unification scheme of radio galaxies and quasars falsified by their observed size distributions
• 3C 17: The BCG of a galaxy cluster at z=0.22
• The unification of powerful quasars and radio galaxies and their relation to other massive galaxies
• Disentangling the AGN and Star-Formation Contributions to the Radio-X-ray Emission of Radio-Loud Quasars at 1<z<2
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• The 3CR $Chandra$ extragalactic survey at 1.0$<z<$1.5
• The far-infrared emission of the radio-loud quasar 3C318