Line-driven disk wind model for ultra-fast outflows in active galactic nuclei -- Scaling with luminosity

TL;DR

This study uses radiation hydrodynamics simulations to model line-driven disk winds in active galactic nuclei, demonstrating their potential to explain ultra-fast outflows and their dependence on black hole mass and Eddington ratio.

Contribution

It provides the first detailed simulation-based analysis linking line-driven disk winds to observed ultra-fast outflows in AGNs, including luminosity scaling relations.

Findings

UFOs are produced in models with specific black hole masses and Eddington ratios.

The scaling relations between wind properties and luminosity match observations.

UFO features are absent in AGNs with very low Eddington ratios.

Abstract

In order to reveal the origin of the ultra-fast outflows (UFOs) that are frequently observed in active galactic nuclei (AGNs), we perform two-dimensional radiation hydrodynamics simulations of the line-driven disk winds, which are accelerated by the radiation force due to the spectral lines. The line-driven winds are successfully launched for the range of $M_{\rm BH}=10^{6-9}M_\odot$ and $\varepsilon$=0.1-0.5, and the resulting mass outflow rate ($\dot{M_{\rm w}}$), momentum flux ($\dot{p_{\rm w}}$), and kinetic luminosity ($\dot{E_{\rm w}}$) are in the region containing 90% of the posterior probability distribution in the $\dot M_{\rm w}$-$L_{\rm bol}$ plane, $\dot p_{\rm w}$-$L_{\rm bol}$ plane, and $\dot E_{\rm w}$-$L_{\rm bol}$ plane shown in Gofford et al., where $M_{\rm BH}$ is the black hole mass, $\varepsilon$ is the Eddington ratio, and $L_{\rm bol}$ is the bolometric luminosity. The best-fitting relations in Gofford et al., $d\log\dot{M_{\rm w}}/d\log{L_{\rm bol}}\sim 0.9$, $d\log\dot{p_{\rm w}}/d\log{L_{\rm bol}}\sim 1.2$, and $d\log\dot{E_{\rm w}}/d\log{L_{\rm bol}}\sim 1.5$, are roughly consistent with our results, $d\log\dot{M_{\rm w}}/d\log{L_{\rm bol}}\sim 9/8$, $d\log\dot{p_{\rm w}}/d\log{L_{\rm bol}}\sim 10/8$, and $d\log\dot{E_{\rm w}}/d\log{L_{\rm bol}}\sim 11/8$. In addition, our model predicts that no UFO features are detected for the AGNs with $\varepsilon \lesssim 0.01$, since the winds do not appear. Also, only AGNs with $M_{\rm BH} \lesssim 10^8 M_\odot$ exhibit the UFOs when $\varepsilon \sim 0.025$. These predictions nicely agree with the X-ray observations (Gofford et al.). These results support that the line-driven disk wind is the origin of the UFOs.