The definitive version is available at www.blackwell-synergy.com.--Copyright Blackwell Publishing-- --DOI : 10.1111/j.1365-2966.2007.11572.xWe have recently shown that X-ray observations of the population of ???low-excitation??? radio galaxies, which includesmost low-power, Fanaroff-Riley class I sources as well as some more powerful Fanaroff-Riley class II objects, are consistent with a model in which the active nuclei of these objects are not radiatively efficient at any waveband. In another recent paper Allen et al. have shown that Bondi accretion of the hot, X-ray emitting phase of the intergalactic medium (IGM) is sufficient to power the jets of several nearby, low-power radio galaxies at the centres of clusters. In this paper we combine these ideas and suggest that accretion of the hot phase of the IGM is sufficient to power all low-excitation radio sources, while highexcitation sources are powered by accretion of cold gas that is in general unrelated to the hot IGM. This model explains a number of properties of the radio-loud active galaxy population, and has important implications for the energy input of radio-loud active galactic nuclei into the hot phase of the IGM: the energy supply of powerful high-excitation sources does not have a direct connection to the hot phase

H 2 pure-rotational emission lines are detected from warm (100-1500 K) molecular gas in 17/55 (31% of) radio galaxies at redshift z < 0.22 observed with the Spitzer IR Spectrograph. The summed H 2 0-038 -2 × 10 42 erg s −1 , yielding warm H 2 masses up to 2 × 10 10 M . These radio galaxies, of both FR radio morphological types, help to firmly establish the new class of radio-selected molecular hydrogen emission galaxies (radio MOHEGs). MOHEGs have extremely large H 2 to 7.7 μm polycyclic aromatic hydrocarbon (PAH) emission ratios: L(H 2 )/L(PAH7.7) = 0.04-4, up to a factor 300 greater than the median value for normal star-forming galaxies. In spite of large H 2 masses, MOHEGs appear to be inefficient at forming stars, perhaps because the molecular gas is kinematically unsettled and turbulent. Low-luminosity mid-IR continuum emission together with low-ionization emission line spectra indicates low-luminosity active galactic nuclei (AGNs) in all but three radio MOHEGs. The AGN X-ray emission measured with Chandra is not luminous enough to power the H 2 emission from MOHEGs. Nearly all radio MOHEGs belong to clusters or close pairs, including four cool-core clusters (Perseus, Hydra, A2052, and A2199). We suggest that the H 2 in radio MOHEGs is delivered in galaxy collisions or cooling flows, then heated by radio-jet feedback in the form of kinetic energy dissipation by shocks or cosmic rays.

We combine Chandra and XMM–Newton X‐ray data from our previous papers with new X‐ray observations and with Spitzer mid‐infrared (mid‐IR) 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‐IR 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 active galactic nucleus (AGN) on such diagnostic diagrams.

The definitive version is available at www.blackwell-synergy.com. Copyright Blackwell Publishing DOI : 10.1111/j.1365-2966.2006.10615.xWe present a Chandra and XMM-Newton spectral analysis of the nuclei of the radio galaxies and radio-loud quasars from the 3CRR sample in the redshift range 0.1 < z < 0.5. In the range of radio luminosity sampled by these objects, mostly FRIIs, it has been clear for some time that a population of radio galaxies (???low-excitation radio galaxies???) cannot easily participate in models that unify narrow-line radio galaxies and broad-line objects. We show that low-excitation and narrow-line radio galaxies have systematically different nuclear Xray properties: while narrow-line radio galaxies universally show a heavily absorbed nuclear X-ray component, such a heavily absorbed component is rarely found in sources classed as low-excitation objects. Combining our data with the results of our earlier work on the z < 0.1 3CRR sources, we discuss the implications of this result for unified models, for the origins of mid-infrared emission from radio sources, and for the nature of the apparent FRI/FRII dichotomy in the X-ray. The lack of direct evidence for accretion-relatedX-ray emission in FRII LERGs leads us to argue that there is a strong possibility that some, or most, FRII LERGs accrete in a radiatively inefficient mode. However, our results are also consistent with a model in which the accretion mode is the same for low- and high-excitation FRIIs, with the lower accretion luminosities in FRII LERGs attributed instead to more efficient radio luminosity production in those objects

We present spectral results from Chandra and XMM-Newton observations of a sample of 22 low-redshift (z < 0:1) radio galaxies and consider whether the core emission originates from the base of a relativistic jet, or an accretion flow, or contains contributions from both. We find correlations between the unabsorbed X-ray, radio, and optical fluxes and luminosities of FR I-type radio-galaxy cores, implying a common origin in the form of a jet. On the other hand, we find that the X-ray spectra of FR II-type radio galaxy cores are dominated by absorbed emission, with N H k 10 23 atoms cm À2 , which is likely to originate in an accretion flow. We discuss several models that may account for the different nuclear properties of FR I-and FR II-type cores and also demonstrate that both heavily obscured, accretion-related and unobscured, jet-related components may be present in all radio galaxy nuclei. Any absorbed, accretion-related components in FR I-type galaxies have low radiative efficiencies.