The influence of radio-galaxy activity on X-ray absorption lines from the intracluster medium

Abstract

We present an investigation of the X-ray absorption features predicted by hydrodynamic simulations of radio galaxies interacting with the intracluster medium (ICM) of their host galaxy clusters. We show how these absorption lines can be used as a new diagnostic for the radio-galaxy/ICM interactions. Such interactions have been observed in numerous systems by ROSAT, CHANDRA and XMM-NEWTON, and understanding them has implications for AGN feedback and galaxy formation. Starting from the hydrodynamic simulations of Reynolds, Heinz & Begelman, we calculate the properties of the highly ionized iron and oxygen lines (seen in absorption against the central active galactic nucleus; AGN), predicting line shapes, equivalent widths, column densities and velocity shifts. The main effect of the jet on the absorption lines is a reduction of the line strength from that of the quiescent ICM and the introduction of some velocity structure in the line profile. We investigate whether these features are detectable with current as well as future high-resolution X-ray spectrometers. We conclude that the CHANDRA transmission gratings have insufficient sensitivity to detect these features with high significance, and certainly would not allow a study of the dynamics of the interaction via absorption signatures. CONSTELLATION-X, on the other hand, will allow superb constraints to be derived. We can also use this analysis to assess the idea that radio-galaxy induced ICM outflows give rise to the resonant oxygen X-ray absorption lines that have been claimed as evidence for the warm-hot intergalactic medium (WHIM). We show that these detached, high-velocity oxygen absorption lines cannot result from a radio-galaxy/ICM interaction, thereby strengthening the WHIM interpretation.