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        X-Ray Nuclei in Radio Galaxies: Exploring the Roles of Hot and Cold Gas Accretion

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        902244.pdf (PDF, 259Kb)
        Author
        Evans, D.A.
        Hardcastle, M.J.
        Croston, J.H.
        Attention
        2299/2136
        Abstract
        We present results from Chandra and XMM-Newton spectroscopic observations of the nuclei of z < 0.5 radio galaxies and quasars from the 3CRR catalog, and examine in detail the dichotomy in the properties of low- and high-excitation radio galaxies. The X-ray spectra of low-excitation sources (those with weak or absent optical emission lines) are dominated by unabsorbed emission from a parsec-scale jet, with no contribution from accretion-related emission. These sources show no evidence for an obscuring torus, and are likely to accrete in a radiatively inefficient manner. High-excitation sources (those with prominent optical emission lines), on the other hand, show a significant contribution from a radiatively efficient accretion disk, which is heavily absorbed in the X-ray when they are oriented close to edge-on with respect to the observer. However, the low-excitation/high-excitation division does not correspond to the FRI/FRII division: thus the Fanaroff-Riley dichotomy remains a consequence of the interaction between the jet and the hot-gas environment through which it propagates. Finally, we suggest that accretion of the hot phase of the IGM is sufficient to power all low-excitation radio sources, while high-excitation sources require an additional contribution from cold gas that in turn forms the cold disk and torus. This model explains a number of properties of the radio-loud active galaxy population, and has important implications for AGN feedback mechanisms.
        Publication date
        2008
        Published in
        In: Extragalactic Jets: Theory and Observation from Radio to Gamma Ray - ASP Conf Series 386
        Other links
        http://hdl.handle.net/2299/2136
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