Ionization Distributions in Outflows of Active Galaxies: Universal Trends and Prospect of Future XRISM Observations

TL;DR

This study analyzes ionization structures in AGN outflows using archival Chandra data, finds correlations with luminosity, and explores future XRISM observations to improve diagnostics of these outflows.

Contribution

It provides the first absorption measure distribution for AGN outflows and assesses XRISM's potential to enhance ionization diagnostics.

Findings

Ionization slope ranges from 0.00 to 0.72.

Anti-correlation between outflow column density and AGN luminosity.

XRISM Resolve can effectively constrain outflow properties with shorter observations.

Abstract

The physics behind the ionization structure of outflows from black holes is yet to be fully understood. Using archival observations with the Chandra\HETG gratings over the past two decades, we measured an absorption measure distribution for a sample of outflows in nine active galaxies (AGNs), namely the dependence of outflow column density, $N_H$, on the ionization parameter, $\xi$. The slope of $\log(N_H)$ vs. $\log\xi$ is found to be between 0.00 and 0.72. We find an anti-correlation between the log of total column density of the outflow and the log of AGN luminosity, and none with the black hole mass and accretion efficiency. A major improvement in the diagnostics of AGN outflows will potentially occur with the launch of the XRISM/Resolve spectrometer. We study the ability of Resolve to reveal the outflow ionization structure by constructing the absorption measure distribution from simulated Resolve spectra, utilizing its superior resolution and effective area. Resolve constrains the column density as well as HETG, but with much shorter observations.