X-ray Simulations of Polar Gas in Accreting Supermassive Black Holes

TL;DR

This study uses ray-tracing simulations to explore how polar gas geometries in active galactic nuclei influence their X-ray spectra, providing benchmarks for future high-resolution X-ray observations.

Contribution

It introduces detailed simulations of polar gas effects on X-ray spectra in AGN, considering different geometries and conditions, which is novel for interpreting upcoming X-ray data.

Findings

Polar gas increases fluorescence line equivalent widths below 5 keV.

Filled cone geometry is inconsistent with observed Type 1 AGN spectra.

Simulations serve as benchmarks for future X-ray instruments like XRISM and Athena.

Abstract

Recent observations have shown that a large portion of the mid--infrared (MIR) spectrum of active galactic nuclei (AGN) stems from the polar regions. In this paper, we investigate the effects of this polar gas on the X-ray spectrum of AGN using ray-tracing simulations. Two geometries for the polar gas are considered, (1) a hollow cone corresponding to the best fit MIR model and (2) a filled cone, both with varying column densities (ranging from $10^{21}-10^{22.5}$ 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 AGN would show signatures of obscuration. We also consider extra emission from the narrow line region such as a scattered power-law with many photoionised 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 on board XRISM and Athena.