Revealing the heavily obscured AGN population with radio
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 21 Aug 2014 HEAD Meeting Chicago
Powerful, FRII Radio Galaxies • 3 CRR, z~1 -2, low-frequency radio-selected • High L/LEdd, log L~1045 -46 ergs-1 • Orientation is dominant variable Cygnus A 21 Aug 2014 HEAD Meeting Chicago
Chandra X-ray Luminosities for NL+BL AGN Log Hard X-ray Luminosity Log Radio Luminosity (5 GHz) • Radio (=AGN) Power comparable • X-ray (“observed”) luminosity of NL sources 10 -1000* lower 21 Aug 2014 HEAD Meeting Chicago
X-ray Hardness Ratio • Simple Unification: – QSO – face-on: bright + soft (Γ~1. 9) – NLRG – edge-on: faint + hard • Exceptions: – 2 QSOs + 1 NLRG: intermediate – 5 soft NLRG z~0. 5 -1, 3 CRRs QSO Soft 21 Aug 2014 HEAD Meeting Chicago NLRG X-ray Hardness Ratio Hard
X-ray Luminosity is obscured Compton Thick • HR hardens as LX decreases • Weakest sources include 2 nd component: soft excess • Possibilities: – Scattered nuclear light – Extended emission (NLR? ) Intermediate QSOs (Wang et al. ) – Jet-related (Hardcastle et al. ) • Obscuration → decrease Lx • Hard to find + measure obscured sources • HR ≠> NH for low LX 21 Aug 2014 HEAD Meeting Chicago Soft NLRG QSOs
Compton Thick? : L[OIII]/LX • 4 soft + 5 hard NLRGs: – high L([OIII]λ 5007)/LX • → 9 Compton Thick (CT) candidates Juneau et al. 2011 • X-ray absorption: – HR → NH~1020 -23 cm-2 – L[OIII]/LX → NH>1024. 5 cm-2 • LX/LR → NH estimate for low S/N sources Edge-on 21 Aug 2014 HEAD Meeting Chicago Radio Core Fraction Face-on
X-ray Absorption vs. Radio Core-Fraction • Strongly correlated • → Observed X-rays are consistent with orientation dependent obscuration of Unified Models Radio Core Fraction Edge-on 21 Aug 2014 HEAD Meeting Chicago Face-on
NH Distribution • NLRG NH peaks at high values, >1024 cm-2 • Consistent with z<1 3 CRRs (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) 21 Aug 2014 HEAD Meeting Chicago
Conclusions • Orientation alone → range of *1000 in observed LX • High S/N X-ray spectra required to accurately estimate intrinsic NH and LX → both generally underestimated • Underestimation of intrinsic LX leads to: – High LX AGN: unobscured, #s underestimated – Low LX AGN: obscured, #s overestimated – Thus: • Luminosity Functions } • Obscured fractions } 21 Aug 2014 increase towards lower LX HEAD Meeting Chicago
Luminosity Function and obscured fraction Mayo & Lawrence 2013 50% covered Change in LF if all are CT 21 Aug 2014 Obscured fraction vs LX HEAD Meeting Chicago
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 21 Aug 2014 HEAD Meeting Chicago
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