Radiation-ionization hydrodynamic simulations of AGN line-driven winds lead to transient shielding and BAL/UFO signatures

Year: 2026

Type: article

Abstract: ABSTRACT Disc winds from active galactic nuclei (AGNs) can be launched by radiation pressure acting on spectral lines. However, launching a line-driven wind in the X-ray-rich environment of AGNs is challenging, as the wind easily gets overionized. Previous simulations suggested that X-ray self-shielding could enable line-driving, though it remained unclear whether this relied on simplified treatments of radiation and ionization. Here, we revisit the X-ray shielding scenario using the first multifrequency multidirectional Monte Carlo radiative photoionization hydrodynamical simulations of AGN line-driven winds. We find that sustaining a steady wind with mass-loss rates of $\approx 20 {{\ \rm per\ cent}}$ of the accretion rate requires an unrealistically weak X-ray flux ($\alpha _{\rm OX}\lt -3$). For stronger X-ray emission ($-3\lt \alpha _{\rm OX}\lt -1$), self-shielding is only transient, leading to episodic ejections with mass-loss rates approaching the accretion rate. Our steady winds naturally produce FeLoBAL, HiBAL, and broad emission-line signatures, depending on the disc spectral energy distribution and the observer’s inclination. At moderate X-ray luminosities ($\alpha _{\rm OX}\sim -3$), transient winds can generate short-lived BAL and ultra-fast outflow (UFO) features. At the highest X-ray luminosities ($\alpha _{\rm OX}\sim -1$), the winds are too ionized to form BALs, but still produce UFOs. These results imply that additional physics is required to explain BAL outflows at realistic X-ray levels and to drive winds strong enough for AGN feedback. None the less, our simulations provide a new framework for interpreting the observed diversity of AGN outflow signatures with fully coupled radiation and dynamics.

Source: Monthly Notices of the Royal Astronomical Society

DOI: 10.1093/mnras/stag592

Authors: Nicolas Scepi, Christian Knigge, Amin Mosallanezhad, Knox S Long, James H Matthews, Stuart A Sim, Austen Wallis

Institutions: Centre National de la Recherche Scientifique, Institut de Planétologie et d'Astrophysique de Grenoble, University of Southampton, Université Grenoble Alpes, Space Telescope Science Institute, Eureka Scientific, University of Oxford, Queen's University Belfast

Language: English

Topic: Galaxies: Formation, Evolution, Phenomena

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $3,046

Funders: National Aeronautics and Space Administration, Space Telescope Science Institute, Jiangsu Hengrui Medicine, Royal Society, University of Southampton, European Commission, Durham University, Science and Technology Facilities Council, H2020 European Research Council

OpenAlex ID: W7160186476