The active nuclei of z<1.0 3CRR radio sources

TL;DR

This study combines multi-wavelength data to analyze the nuclei of radio galaxies and quasars below redshift 1, revealing the nature of their active nuclei and differences in absorption properties, with implications for black hole activity diagnostics.

Contribution

It provides a comprehensive analysis of radio-loud AGN nuclei using combined X-ray and infrared data, clarifying the presence of radiatively efficient nuclei and the nature of soft X-ray components.

Findings

Most low-excitation radio galaxies lack radiatively efficient nuclei.

Absorbing column distributions differ from radio-quiet quasars and Seyfert 2s.

Jet origin is likely for the soft X-ray component.

Abstract

We combine Chandra and XMM-Newton X-ray data from our previous papers with new X-ray observations and with Spitzer mid-infrared data in order to study the nature of the nuclei of radio galaxies and radio-loud quasars with z<1.0 from the 3CRR sample. The significant increase in sample size over our previous work, the reduction of bias in the sample as a result of new observations, and the availability of more mid-infrared data allow us to show conclusively that almost all objects classed as low-excitation radio galaxies in optical spectroscopic studies lack a radiatively efficient active nucleus. We show that the distribution of absorbing columns in the narrow-line radio galaxies differs from the population of X-ray-selected radio-quiet type-2 quasars and from that in local Seyfert 2s. We comment on the current evidence for the nature of the soft X-ray component in radio-galaxy nuclear spectra, concluding that a jet origin for this component is very hard to evade. Finally, we discuss the recently discovered `fundamental plane' of black hole activity, showing that care must be taken when placing radio-loud AGN on such diagnostic diagrams.