Astrophys. J., 773, 15 (2013/August-2)
Revealing the heavily obscured active galactic nucleus population of high-redshift 3CRR sources with Chandra X-ray observations.
WILKES B.J., KURASZKIEWICZ J., HAAS M., BARTHEL P., LEIPSKI C., WILLNER S.P., WORRALL D.M., BIRKINSHAW M., ANTONUCCI R., ASHBY M.L.N., CHINI R., FAZIO G.G., LAWRENCE C., OGLE P. and SCHULZ B.
Abstract (from CDS):
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 LX∼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 LX∼43-45), and mostly hard X-ray hardness ratios (HR >0) indicating obscuration (NH∼1022-1024/cm2). 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/cm2 < NH(int) <1.5x1024/cm2) to CT (NH(int) >1.5x1024/cm2) 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 10-1000xhigher than indicated by their X-ray hardness ratios, and their true LX values are ∼10-100x larger than the hardness-ratio absorption corrections would indicate.
quasars: general - X-rays: galaxies
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