REVEALING THE HEAVILY OBSCURED ACTIVE GALACTIC NUCLEUS POPULATION OF HIGH-REDSHIFT 3CRR SOURCES WITH CHANDRA X-RAY OBSERVATIONS

Belinda J. Wilkes*, Joanna Kuraszkiewicz, Martin Haas, Peter Barthel, Christian Leipski, S. P. Willner, D. M. Worrall, Mark Birkinshaw, Robert Antonucci, M. L. N. Ashby, Rolf Chini, G. G. Fazio, Charles Lawrence, Patrick Ogle, Bernhard Schulz

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

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Abstract

Chandra observations of a complete, flux-limited sample of 38 high-redshift (1 < z < 2), low-frequency-selected (and so unbiased in orientation) 3CRR radio sources are reported. The sample includes 21 quasars (=broad-line radio galaxies) and 17 narrow-line radio galaxies (NLRGs) with matched 178 MHz radio luminosity (log LR (5 GHz) ∼44-45). The quasars have high radio core fraction, high X-ray luminosities (log L X ∼45-46), and soft X-ray hardness ratios (HR ∼-0.5) indicating low obscuration. The NLRGs have lower core fraction, lower apparent X-ray luminosities (log L X ∼43-45), and mostly hard X-ray hardness ratios (HR >0) indicating obscuration (N H ∼1022-1024 cm -2). These properties and the correlation between obscuration and radio core fraction are consistent with orientation-dependent obscuration as in unification models. About half the NLRGs have soft X-ray hardness ratios and/or a high [O III] emission line to X-ray luminosity ratio suggesting obscuration by Compton thick (CT) material so that scattered nuclear or extended X-ray emission dominates (as in NGC 1068). The ratios of unobscured to Compton-thin (1022 cm-2 < N H (int) <1.5 × 1024 cm-2) to CT (N H (int) >1.5 × 1024 cm-2) is 2.5:1.4:1 in this high-luminosity, radio-selected sample. The obscured fraction is 0.5, higher than is typically reported for active galactic nuclei at comparable luminosities from multi-wavelength surveys (0.1-0.3). Assuming random nuclear orientation, the unobscured half-opening angle of the disk/wind/torus structure is ∼60° and the obscuring material covers 30°, ∼12° of which is CT. The multi-wavelength properties reveal that many NLRGs have intrinsic absorption 10-1000 × higher than indicated by their X-ray hardness ratios, and their true L X values are ∼10-100× larger than the hardness-ratio absorption corrections would indicate. 

Original languageEnglish
Article number15
Pages (from-to)1-16
Number of pages16
JournalAstrophysical Journal
Volume773
Issue number1
Early online date19 Jul 2013
DOIs
Publication statusPublished - 10 Aug 2013

Bibliographical note

16 pages, 11 figures, 3 tables; ApJ, in press

Keywords

  • quasars: general
  • X-rays: galaxies
  • COMPACT STEEP-SPECTRUM
  • XMM-NEWTON OBSERVATIONS
  • POWERFUL RADIO GALAXIES
  • DIGITAL SKY SURVEY
  • EXTRAGALACTIC LEGACY SURVEY
  • DUAL-FREQUENCY OBSERVATIONS
  • SUPERMASSIVE BLACK-HOLES
  • EXTENDED GROTH STRIP
  • SEYFERT 2 GALAXIES
  • DEEP FIELD SOUTH

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