Line-driven disc wind model for ultrafast outflows in active galactic nuclei – scaling with luminosity

Abstract

In order to reveal the origin of the ultrafast outflows (UFOs) that are frequently observed in active galactic nuclei (AGNs), we perform two-dimensional radiation hydrodynamics simulations of the line-driven disc winds, which are accelerated by the radiation force due to the spectral lines. The line-driven winds are successfully launched for the range of MBH = 106–9 M⊙ and ε = 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 per cent of the posterior probability distribution in the |$\dot{M}_{\rm w}$|–Lbol plane, |$\dot{p}_{\rm w}$|–Lbol plane, and |$\dot{E}_{\rm w}$|–Lbol plane shown in Gofford et al., where MBH is the black hole mass, ε is the Eddington ratio, and Lbol is the bolometric luminosity. The best-fitting relations in Gofford et al., |${\rm d}\log \dot{M_{\rm w}}/{\rm d}\log {L_{\rm bol}}\sim 0.9$|⁠, |${\rm d}\log \dot{p_{\rm w}}/{\rm d}\log {L_{\rm bol}}\sim 1.2$|⁠, and |${\rm d}\log \dot{E_{\rm w}}/{\rm d}\log {L_{\rm bol}}\sim 1.5$|⁠, are roughly consistent with our results, |${\rm d}\log \dot{M_{\rm w}}/{\rm d}\log {L_{\rm bol}}\sim 9/8$|⁠, |${\rm d}\log \dot{p_{\rm w}}/{\rm d}\log {L_{\rm bol}}\sim 10/8$|⁠, and |${\rm d}\log \dot{E_{\rm w}}/{\rm d}\log {L_{\rm bol}}\sim 11/8$|⁠. In addition, our model predicts that no UFO features are detected for the AGNs with ε ≲ 0.01, since the winds do not appear. Also, only AGNs with MBH ≲ 108 M⊙ exhibit the UFOs when ε ∼ 0.025. These predictions nicely agree with the X-ray observations. These results support that the line-driven disc wind is the origin of the UFOs.