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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,

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Presentation on theme: "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,"— Presentation transcript:

1 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

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

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 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 Why Observe in Infrared?

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 LOBEJETDUSTACCRETION DISK RadioMicrowave Sub-mm InfraredVisible Low-frequency radio emission from lobes is ISOTROPIC FRII radio sources uniquely useful in separating intrinsic from apparent differences

9 The Spitzer Sample 3CRR extremely powerful radio sources, selected for: –Radio-lobe rest luminosity L > W/Hz/sr –Redshift, 0.416 Quasars, 18 Galaxies Orientation-unbiased sample IRS long low spectra,  m MIPS photometry, 24, 70 & 160  m

10 IRS Spectra QuasarsGalaxies 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, f therm = L therm /L total 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

21 Testing Unification Compare quasar and galaxy luminosity Normalise by radio luminosity (R dr = L dust /L radio ) –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 (R dr = L dust /L radio ) –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 (L 24 > 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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