High-redshift Faranoff–Riley type II radio galaxies: X-ray properties of the cores |
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| Authors: | E Belsole D M Worrall M J Hardcastle |
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| Institution: | Department of Physics, University of Bristol, Tyndall Avenue, Bristol BS8 1TL;School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB |
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| Abstract: | We present an extensive X-ray spectral analysis of the cores of 19 Faranoff–Riley type II sources in the redshift range 0.5 < z < 1.0 which were selected to be matched in isotropic radio power. The sample consists of 10 radio galaxies (RGs) and nine quasars. We compare our results with the expectations from a unification model that ascribes the difference between these two types of sources to the viewing angle to the line of sight, beaming and the presence of a dust and gas torus. We find that the spectrum of all the quasars can be fitted with a single power law, and that the spectral index flattens with decreasing angle to the line of sight. We interpret this as the effect of increasingly dominant inverse Compton X-ray emission, beamed such that the jet emission outshines other core components. For up to 70 per cent of the RGs we detect intrinsic absorption; their core spectra are best fitted with an unabsorbed steep power law of average spectral index Γ= 2.1 and an absorbed power law of spectral index Γ= 1.6, which is flatter than that observed for radio-quiet quasars (RQQs). We further conclude that the presence of a jet affects the spectral properties of absorbed nuclear emission in active galactic nuclei. In RGs, any steep-spectrum component of nuclear X-ray emission, similar to that seen in RQQs, must be masked by a jet or by jet-related emission. |
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| Keywords: | galaxies: active galaxies: high-redshift galaxies: nuclei quasars: general radio continuum: galaxies X-rays: galaxies |
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