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  • Beyond Simple AGN Unificati...
    Kuraszkiewicz, Joanna; Wilkes, Belinda J.; Atanas, Adam; Buchner, Johannes; McDowell, Jonathan C.; Willner, S. P.; Ashby, Matthew L. N.; Azadi, Mojegan; Barthel, Peter; Haas, Martin; Worrall, Diana M.; Birkinshaw, Mark; Antonucci, Robert; Chini, Rolf; Fazio, Giovanni G.; Lawrence, Charles; Ogle, Patrick

    Astrophysical journal/˜The œAstrophysical journal, 06/2021, Volume: 913, Issue: 2
    Journal Article

    Abstract 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 N H , 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 N H < 10 22 cm −2 . Multiwavelength analysis suggests that these objects have lower L / L Edd than typical NLRGs at similar orientation. Thus, both orientation and L / L Edd 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 / L Edd extending to lower values in this sample. In contrast, at high redshifts, the narrower range and high L / L Edd values allowed orientation (and so simple unification) to dominate the sample’s observed properties.