Spitzer Observations of 3C Quasars and Radio Galaxies: Mid-Infrared Properties of Powerful Radio Sources

By K. Cleary, Charles R. Lawrence, J. Marshall, L. Hao, D. Laboratory, C. I. O. Technology., Cornell University. 2006

133 citations recorded by the source corpus.

We have measured mid-infrared radiation from an orientation-unbiased sample of 3CRR galaxies and quasars at redshifts 0.4 ≤ z ≤ 1.2 with the IRS and MIPS instruments on Spitzer. Powerful emission (L24 μm > 1022.4 W Hz-1 sr-1) was detected from all but one of the sources. We fit the Spitzer data and other measurements from the literature with synchrotron and dust components. The IRS data provide powerful constraints on the fits. At 15 μm, quasars are typically 4 times brighter than radio galaxies with the same isotropic radio power. Based on our fits, half of this difference can be attributed to the presence of nonthermal emission in the quasars but not the radio galaxies. The other half is consistent with dust absorption in the radio galaxies but not the quasars. Fitted optical depths are anticorrelated with core dominance, from which we infer an equatorial distribution of dust around the central engine. The median optical depth at 9.7 μm for objects with core dominance factor R > 10-2 is ≈0.4; for objects with R ≤ 10-2, it is ≈1.1. We have thus addressed a long-standing question in the unification of FR II quasars and galaxies: quasars are more luminous in the mid-infrared than galaxies because of a combination of Doppler-boosted synchrotron emission in quasars and extinction in galaxies, both orientation-dependent effects.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/99a5b85d0145854cbd690aa12ea1ee32a360909e

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Citations in the corpus

CONSTRAINING EMISSION MODELS OF LUMINOUS BLAZAR SOURCES (2009, background): “According to Cleary et al. (2007), who analyzed Spitzer observations of 3C quasars, the dust temperatures are in the range, T ∼ 100–300 K.”
The blazar sequence: a new perspective (2008, background): “From the result of Cleary et al. (2007) we then set RIR = 2.5 × 1018 L1/2disc,45 cm. (7) The corresponding radiation energy density, as measured in the comoving frame, is U ′IR = 3 × 10−4 2 erg cm−3.”
The active nuclei of z < 1.0 3CRR radio sources (2009, background): “In the IR, the 3CRR objects in this redshift range have been studied by Ogle et al. (2006) and Cleary et al. (2007).”
IDENTIFYING LUMINOUS ACTIVE GALACTIC NUCLEI IN DEEP SURVEYS: REVISED IRAC SELECTION CRITERIA (2012, background): “This suggests that the radio-based comparison may be biased, at least in part, by the contribution from beamed synchrotron emission in Type 1 AGN (Cleary et al. 2007).”
Canonical high power blazars (2009, background): “Our approach follows in part the results of Cleary et al. (2007), finding weak sign of hot dust emission in the studied spectra, and partly is dictated by simplicity.”
FERMI/LARGE AREA TELESCOPE DISCOVERY OF GAMMA-RAY EMISSION FROM A RELATIVISTIC JET IN THE NARROW-LINE QUASAR PMN J0948+0022 (2009, background): “Its distance is assumed to be RIR = 2.5 × 10 18L 1/2 disk,45 cm, calculated by considering that the dust is at the temperature of 370 K (see Cleary et al. 2007), where is the maximum of efficiency in reprocessing the impinging photons into IR radiation.”