Relativistic accretion disc reflection in AGN X-ray spectra at z = 0.5-4: a study of four Chandra Deep Fields

We confirm that the spectra are best fit by a model containing two Compton reflection components, one from distant material, and the other displaying relativistic broadening, most likely from the inner accretion disc. The degree of relativistic broadening indicates a preference for high black hole spin, but the reflection is weaker than that expected for a flat disc illuminated by a point source. We investigate the Compton reflection signatures as a function of luminosity, redshift, and obscuration, confirming an X-ray Baldwin effect for both the narrow and broad components of the iron line. Anticorrelations are also seen with redshift and obscuring column density, but are difficult to disentangle from the Baldwin effect. Our methodology is able to extract information from multiple spectra with low signal-to-noise ratio (SN), and can be applied to future data sets such as eROSITA. We show using simulations, however, that it is necessary to apply an appropriate S/N cut to the samples to ensure the spectra add useful information.