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

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 Xray 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.

A multiwavelength-motivated X-ray model for the Circinus Galaxy

“…For example, Mn K𝛼 at 5.88 keV was identified as Cr XXIV in Arévalo et al (2014) using MYT , while it is naturally produced by our model. The accretion disk and the BLR can strongly affect the reprocessed continuum emission and the Fe K𝛼 complex, while the polar component is expected to contribute significantly to the AGN emission at 𝐸 5 keV McKaig et al (2021), enhancing the flux of some of the emission lines (e.g., Liu et al 2019;McKaig et al 2021).…”

“…This emission could be related, at least in some cases, to the polar dust observed in the MIR (e.g., Liu et al 2019). It has been also suggested that the polar component might be responsible for some of the narrow emission features observed at 𝐸 3 keV in heavily obscured AGN, such as the Si K𝛼 line (e.g., Liu et al 2019;McKaig et al 2021).…”