X-ray simulations of polar gas in accreting supermassive black holes

Abstract

ABSTRACT Recent observations have shown that a large portion of the mid-infrared (MIR) spectrum of active galactic nuclei (AGNs) stems from the polar regions. In this paper, we investigate the effects of this polar gas on the X-ray spectrum of AGNs using ray-tracing simulations. Two geometries for the polar gas are considered, (1) a hollow cone corresponding to the best-fitting MIR model and (2) a filled cone, both with varying column densities (ranging from 1021 to 1022.5 cm−2) along with a torus surrounding the central X-ray source. We find that the polar gas leads to an increase in the equivalent width of several fluorescence lines below ∼5 keV (e.g. O, Ne, Mg, Si). A filled geometry is unlikely for the polar component, as the X-ray spectra of many type 1 AGNs would show signatures of obscuration. We also consider extra emission from the narrow-line region such as a scattered power law with many photoionized lines from obscured AGNs, and different opening angles and matter compositions for the hollow cone. These simulations will provide a fundamental benchmark for current and future high spectral resolution X-ray instruments, such as those onboard XRISM and Athena.