Relativistic accretion disk reflection in AGN X-ray spectra at z=0.5--4: a study of four \textit{Chandra} deep fields

TL;DR

This study analyzes X-ray spectra of AGN at redshifts 0.5 to 4, revealing relativistic disk reflection features, high black hole spins, and effects of luminosity, redshift, and obscuration on reflection signatures.

Contribution

It introduces a methodology to extract reflection information from low signal-to-noise spectra and investigates the dependence of reflection features on various AGN properties.

Findings

Detection of relativistic broadening indicating high black hole spins.

Confirmation of the X-ray Baldwin effect for iron line components.

Anti-correlations of reflection strength with redshift and obscuration.

Abstract

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 disk. The degree of relativistic broadening indicates a preference for high black hole spin, but the reflection is weaker than that expected for a flat disk 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. Anti-correlations 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, and can be applied to future data sets such as eROSITA. We show using simulations, however, that it is necessary to apply an appropriate signal-to-noise ratio cut to the samples to ensure the spectra add useful information.