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Revealing the heavily obscured AGN population with radio selection

This study aims to find all AGN by utilizing radio selection methods. The orientation of the AGN is found to be a dominant variable, and the Compton thick AGN candidates are identified. The NH distribution and the correlation between X-ray absorption and radio core fraction are discussed.

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Revealing the heavily obscured AGN population with radio selection

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  1. 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 Chicago

  2. 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 Chicago

  3. 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 Chicago

  4. X-ray Hardness Ratio QSO z~0.5-1, 3CRRs NLRG • Simple Unification: • QSO – face-on: bright + soft (Γ~1.9) • NLRG – edge-on: faint + hard • Exceptions: • 2 QSOs + 1 NLRG: intermediate • 5 soft NLRG Soft Hard X-ray Hardness Ratio HEAD Meeting Chicago

  5. Compton Thick X-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 Soft NLRG QSOs HEAD Meeting Chicago

  6. 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 Chicago

  7. Radio Core Fraction X-ray Absorption vs. Radio Core-Fraction • Strongly correlated • → Observed X-rays are consistent with orientation dependent obscuration of Unified Models Edge-on Face-on HEAD Meeting Chicago

  8. 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 Chicago

  9. Conclusions • 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 Chicago

  10. Luminosity Function and obscured fraction Mayo & Lawrence 2013 50% covered Change in LF if all are CT Obscured fraction vs LX HEAD Meeting Chicago

  11. Conclusions • 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 Chicago

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