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Journal Article

Beyond simple AGN unification with Chandra-observed 3CRR sources at 0.5 < z < 1


Buchner,  Johannes
High Energy Astrophysics, MPI for Extraterrestrial Physics, Max Planck Society;

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Kuraszkiewicz, J., Wilkes, B. J., Atanas, A., Buchner, J., McDowell, J. C., Willner, S. P., et al. (2021). Beyond simple AGN unification with Chandra-observed 3CRR sources at 0.5 < z < 1. The Astrophysical Journal, 913(2): 134. doi:10.3847/1538-4357/abf3c0.

Cite as: https://hdl.handle.net/21.11116/0000-0009-2372-F
Low-frequency radio selection finds radio-bright galaxies regardless of the amount of obscuration by gas and dust. We report Chandra observations of a complete 178 MHz–selected, and so orientation-unbiased, sample of 44 0.5 < z < 1 3CRR sources. The sample is comprised of quasars and narrow-line radio galaxies (NLRGs) with similar radio luminosities, and the radio structure serves as both an age and an orientation indicator. Consistent with unification, intrinsic obscuration (measured by NH, X-ray hardness ratio, and X-ray luminosity) generally increases with inclination. However, the sample includes a population not seen in high-z 3CRR sources: NLRGs viewed at intermediate inclination angles with NH < 1022 cm−2. Multiwavelength analysis suggests that these objects have lower L/LEddthan typical NLRGs at similar orientation. Thus, both orientation and L/LEdd are important, and a "radiation-regulated unification" provides a better explanation of the sample's observed properties. In comparison with the 3CRR sample at 1 < z < 2, our lower-redshift sample shows a higher fraction of Compton-thin NLRGs (45% versus 29%) but a similar Compton-thick fraction (20%), implying a larger covering factor of Compton-thin material at intermediate viewing angles and thus a more "puffed-up" torus atmosphere. We posit that this is due to a range of L/LEdd extending to lower values in this sample. In contrast, at high redshifts, the narrower range and high L/LEdd values allowed orientation (and so simple unification) to dominate the sample's observed properties.