revealing the heavily obscured agn population with radio selection
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Revealing the heavily obscured AGN population with radio selection. Aim: to find ALL the AGN. Wilkes, Kuraszkiewicz , Atanas , Haas, Barthel , Willner , Leipski , Worrall Birkinshaw , Antonucci,Ogle , U.T. Cobley & all. Powerful, FRII Radio Galaxies.

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revealing the heavily obscured agn population with radio selection

Revealing the heavily obscured AGN population with radio selection

Aim: to find ALL the AGN

Wilkes, Kuraszkiewicz, Atanas,

Haas, Barthel, Willner, Leipski, Worrall Birkinshaw, Antonucci,Ogle,

U.T. Cobley& all

HEAD Meeting


powerful frii radio galaxies
Powerful, FRII Radio Galaxies
  • 3CRR, z~1-2, low-frequency radio-selected
  • High L/LEdd, log L~1045-46 ergs-1
  • Orientation is dominant variable

Cygnus A

HEAD Meeting


chandra x ray luminosities for nl bl agn
Chandra X-ray Luminosities for NL+BL AGN

Log Hard X-ray Luminosity

Log Radio Luminosity (5GHz)

  • Radio (=AGN) Power comparable
  • X-ray (“observed”) luminosity of NL sources 10-1000* lower

HEAD Meeting


x ray hardness ratio
X-ray Hardness Ratio


z~0.5-1, 3CRRs


  • Simple Unification:
    • QSO – face-on: bright + soft (Γ~1.9)
    • NLRG – edge-on: faint + hard
  • Exceptions:
    • 2 QSOs + 1 NLRG: intermediate
    • 5 soft NLRG



X-ray Hardness Ratio

HEAD Meeting


x ray luminosity is obscured
Compton ThickX-ray Luminosity is obscured
  • HR hardens as LX decreases
  • Weakest sources include 2ndcomponent: soft excess
  • Possibilities:
    • Scattered nuclear light
    • Extended emission (NLR?) (Wang et al.)
    • Jet-related (Hardcastle et al.)
  • Obscuration → decrease Lx
  • Hard to find + measure obscured sources
  • HR ≠> NH for low LX

Intermediate QSOs



HEAD Meeting


compton thick l oiii l x
Compton Thick? : L[OIII]/LX
  • 4 soft + 5 hard NLRGs:
    • high L([OIII]λ5007)/LX
  • → 9 Compton Thick (CT) candidates
  • X-ray absorption:
    • HR → NH~1020-23cm-2
    • L[OIII]/LX→ NH>1024.5cm-2
  • LX/LR → NHestimate for low S/N sources

Juneau et al. 2011

Edge-on Radio Core Fraction Face-on

HEAD Meeting


x ray absorption vs radio core fraction
Radio Core FractionX-ray Absorption vs. Radio Core-Fraction
  • Strongly correlated
  • → Observed X-rays are consistent with orientation dependent obscuration of Unified Models



HEAD Meeting


n h distribution
NH Distribution
  • NLRG NH peaks at high values, >1024cm-2
  • Consistent with z<1 3CRRs

(Hardcastle et al 2009)

  • Obscured fraction ~ 0.5 higher than typical 0.1-0.3 for high Luminosity AGN
  • CT fraction ~ 0.2
  • Consistent with CXRB models (Gilli et al. 2007)

HEAD Meeting


  • Orientation alone → range of *1000 in observed LX
  • High S/N X-ray spectra required to accurately estimate intrinsic NHand LX → both generally underestimated
  • Underestimation of intrinsic LX leads to:
    • High LXAGN: unobscured, #s underestimated
    • Low LX AGN: obscured, #s overestimated
    • Thus:
      • Luminosity Functions } increase towards lower LX
      • Obscured fractions }

HEAD Meeting


luminosity function and obscured fraction
Luminosity Function and obscured fraction

Mayo & Lawrence 2013

50% covered

Change in LF if all are CT

Obscured fraction vs LX

HEAD Meeting


  • Luminosity Functions may be flatter, high luminosity active galaxies more numerous than currently deduced
  • A luminosity-dependent obscured fraction may not be required to explain X-ray and optical data

Take care when estimating obscuration for sources in X-ray samples

HEAD Meeting