Beyond Simple AGN Unification with Chandra-observed 3CRR Sources

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 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 h~$<10^{22}$~cm$^{-2}$. Multiwavelength analysis suggests these objects have lower $L/L_{rm Edd}$ than typical NLRGs at similar orientation. Thus both orientation and $L/L_{rm Edd}$ are important, and a radiation-regulated Unification provides a better explanation of the samples 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% vs. 29%) but similar Compton-thick fraction (20%), implying a larger covering factor of Compton-thin material at intermediate viewing angles and so a more puffed-up torus atmosphere. We posit that this is due to a range of $L/L_{rm Edd}$ extending to lower values in this sample. In contrast, at high redshifts the narrower range and high $L/L_{rm Edd}$ values allowed orientation (and so simple Unification) to dominate the samples observed properties.