AGN contamination of galaxy-cluster thermal X-ray emission: predictions for eRosita from cosmological simulations

TL;DR

This paper models the X-ray emission from simulated SMBHs to predict AGN contamination in galaxy cluster observations by eROSITA, revealing significant AGN influence on cluster detection at high redshifts.

Contribution

It provides the first detailed simulation-based predictions of AGN contamination in galaxy cluster X-ray observations for eROSITA, incorporating realistic obscuration and synthetic data.

Findings

AGN luminosity functions match observations up to z~2

Significant AGN contamination in cluster X-ray flux at z~1-1.5

Predicted AGN counts can exceed ICM emission by over a factor of 2

Abstract

In this study, we present a modelling of the X-ray emission from the simulated SMBHs within the cosmological hydrodynamical Magneticum Pathfinder Simulation, in order to study the statistical properties of the resulting X-ray Active Galactic Nuclei (AGN) population and their expected contribution to the X-ray flux from galaxy clusters. The simulations reproduce the evolution of the observed unabsorbed AGN bolometric luminosity functions (LFs) up to redshift z~2, consistently with previous works. Furthermore, we study the evolution of the LFs in the soft (SXR) and hard (HXR) X-ray bands by means of synthetic X-ray data generated with the PHOX simulator, that includes an observationally-motivated modelling of an instrinsic absorption component, mimicking the torus around the AGN. The reconstructed SXR and HXR AGN LFs present a remarkable agreement with observational data up to z~2 when an additional obscuration fraction for Compton-thick AGN is assumed, although a discrepancy still exists for the SXR LF at z=2.3. With this approach, we also generate full eROSITA mock observations to predict the level of contamination due to AGN of the intra-cluster medium (ICM) X-ray emission, which can affect cluster detection especially at high redshifts. We find that, at z~1-1.5, for 20-40% of the clusters with M500>3e13 Msun/h, the AGN counts in the observed SXR band exceed by more than a factor of 2 the counts from the whole ICM.