Expanded Iron UTA spectra -- probing the thermal stability limits in AGN clouds

TL;DR

This paper presents new atomic data for Fe XIV, XV, and XVI ions, improving the modeling of Fe UTAs in AGN spectra and exploring their thermal stability and density dependence.

Contribution

It provides updated energies and oscillator strengths for key Fe ions and integrates them into Cloudy to analyze AGN absorption features.

Findings

Fe XIV UTA absorption profile varies with density

Updated atomic data enhances AGN spectral modeling

Thermal stability of AGN clouds is influenced by Fe UTA features

Abstract

The Fe unresolved transition array (UTAs) produce prominent features in the 15-17?A wavelength range in the spectra of Active Galactic Nuclei (AGN). Here we present new calculations of the energies and oscillator strengths of inner- shell lines from Fe XIV, Fe XV, and Fe XVI. These are crucial ions since they are dominant at inflection points in the gas thermal stability curve, and UTA excitation followed by autoionization is an important ionization mechanism for these species. We incorporate these, and data reported in previous papers, into the plasma simulation code Cloudy. This updated physics is subsequently employed to reconsider the thermally stable phases in absorbing media in Active Galactic Nuclei. We show how the absorption profile of the Fe XIV UTA depends on density, due to the changing populations of levels within the ground configuration.