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Spitzer Observations of 3C Quasars and Radio Galaxies:

Spitzer Observations of 3C Quasars and Radio Galaxies: Mid-Infrared Properties of Powerful Radio Sources. K. Cleary 1 , C.R. Lawrence 1 , J.A. Marshall 2 , L. Hao 2 , D. Meier 1. 1: JPL, California Institute of Technology 2: Cornell University. Summary. Why observe in infrared? Previous Work

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Spitzer Observations of 3C Quasars and Radio Galaxies:

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  1. Spitzer Observations of 3C Quasars and Radio Galaxies: Mid-Infrared Properties of Powerful Radio Sources K. Cleary1, C.R. Lawrence1, J.A. Marshall2, L. Hao2, D. Meier1 1: JPL, California Institute of Technology2: Cornell University

  2. Summary • Why observe in infrared? • Previous Work • The Spitzer Sample • Spectral Fitting • Results

  3. Why Observe in Infrared? • Barthel (1989) - FR II RG are quasars with BH hidden behind obscuring dusty torus • Hidden quasar light is reprocessed and emitted at longer wavelengths • Signature of warm dust should be detectable in infrared • FIR should be orientation independent

  4. Why Observe in Infrared? • Implies direct test of FRII/Quasar unification • Quasars and Galaxies should have similar infrared luminosity • Need to normalise by radio lobe luminosity to account for varying central engine power

  5. Previous Work • IRAS • Heckman et al. (1992), 6/117 RG and quasars, 3C z>0.3 • Quasars 3x more luminous (normalised) than galaxies • Confirmed by Hes et al. (1995) • IRAS 60 um quasars systematically brighter than galaxies • Beamed component may account for this difference • Hoekstra et al (1997) • IRAS 60 um fluxes consistent with an orientation-based model • Other processes such as optical depth also contribute

  6. Previous Work • ISO • van Bemmel et al. (2000) • 4 3C Q/G pairs matched in redshift and radio power • Non-thermal contribution estimated at < 2% • Systematic excess found for quasars • Meisenheimer et al. (2001) • 10 3C Q/G pairs • Dust luminosity distribution (normalised by radio power) similar for quasars and galaxies • Andreani et al (2002) • ISO photometry and mm data for sample of 3C quasars and galaxies • Quasar composite spectrum 3x brighter than galaxy spectrum in mm region • Haas et al. (2004) • 3CR 17/51 galaxies, 17/24 quasars, • similar normalised restframe 70 micron luminosities

  7. Previous Work Both Beamed synchrotron emission and Dust extinction Modulate IR emission of quasars and galaxies to some degree. • Spitzer provides additional constraints: • increased photometric sensitivity • MIR spectroscopic data • Allows us to quantify these effects in orientation-unbiased sample

  8. FRII SED LOBE JET DUST ACCRETION DISK • Low-frequency radio emission from lobes is ISOTROPIC • FRII radio sources uniquely useful in separating intrinsic from apparent differences Radio Microwave Sub-mm Infrared Visible

  9. The Spitzer Sample • 3CRR extremely powerful radio sources, selected for: • Radio-lobe rest luminosity L > 1026 W/Hz/sr • Redshift, 0.4<z<1.2 • Ecliptic latitude (for Spitzer scheduling) • =>16 Quasars, 18 Galaxies • Orientation-unbiased sample • IRS long low spectra, 15-37 m • MIPS photometry, 24, 70 & 160 m

  10. Quasars Galaxies IRS Spectra • Basic Morphology • Silicate Emission • Silicate Absorption • Emission Lines

  11. Characteristic Luminosities • Characteristic Luminosities (W/Hz/sr) • 15 microns from IRS • 30 microns from MIPS

  12. Origin of IR Emission • Thermal • Dust heated by star-formation • Dust heated by “central engine” • Non-thermal • Synchrotron from radio lobes • Synchrotron from radio jet

  13. Spectral Components Lobe Jet Dust

  14. Spectral Fitting • For all objects with IRS spectra, we fit the following components: • Warm dust + lobe synchrotron • Warm dust + lobe synchrotron + jet synchrotron • Warm dust + lobe synchrotron + cool dust • Warm dust + cool dust + lobe synchrotron + jet synchrotron • Combination with best chi-squared selected

  15. Spectral Fits Galaxy 3C 184 SED IRS Spectrum

  16. Spectral Fits Quasar 3C 138 SED IRS Spectrum

  17. Fit Parameters • Synchrotron fitting functions • Dust model • Temperature • Optical Depth • Thermal fraction, ftherm = Ltherm/Ltotal • Can correct observed MIR flux density for non-thermal emission • At 15 microns, up to 90% non-thermal for some quasars

  18. Thermal fraction

  19. Non-thermal correction

  20. Non-thermal correction

  21. Testing Unification • Compare quasar and galaxy luminosity • Normalise by radio luminosity (Rdr = Ldust/Lradio) • Quasars 4 times brighter than galaxies at 15 microns • Correct for non-thermal emission • Quasars on 2 times brighter than galaxies • Correct for extinction • Quasars and galaxies have same average brightness

  22. Testing Unification • Compare quasar and galaxy luminosity • Normalise by radio luminosity (Rdr = Ldust/Lradio) • Quasars 4 times brighter than galaxies at 15 microns • Correct for non-thermal emission • Quasars on 2 times brighter than galaxies • Correct for extinction • Quasars and galaxies have same average brightness

  23. Role of Orientation • Anticorrelation between optical depth and core dominance • R<10-2, Median(tau)=1.1 • R>10-2, Median(tau)=0.4 • Infer equatorial distribution of dust • Consistent with ‘dusty torus’ of unification schemes.

  24. Summary • We have observed an orientation-unbiased sample of extremely powerful 3CRR radio galaxies and quasars • Detected powerful MIR emission (L24 > 1022.4 W/Hz/sr) • IRS measurements provide powerful constraints on SED • Allowed us to fit continuum synchrotron and dust components

  25. Summary • Non-thermal contribution to MIR up to 90% in some quasars • At 15 microns, quasars are typically 4 times brighter than galaxies with same isotropic radio power • Half of this difference is due to non-thermal emission present in quasars but not in galaxies • Other half is due to absorption in galaxies but not in quasars

  26. Conclusion • We have addressed a long-standing question in AGN unification • Quasars are more luminous IR emitters than galaxies because of: • Doppler boosted synchrotron in quasars • Extinction from dusty torus in galaxies • Both orientation-dependent effects

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