Winds and feedback from supermassive black holes accreting at low rates: Hydrodynamical treatment (1905.13708v2)

Abstract: Outflows produced by a supermassive black hole (SMBH) can have important feedback effects in its host galaxy. An unresolved question is the nature and properties of winds from SMBHs accreting at low rates in low-luminosity active galactic nuclei (LLAGNs). We performed two-dimensional numerical, hydrodynamical simulations of radiatively inefficient accretion flows onto non spinning black holes. We explored a diversity of initial conditions in terms of rotation curves and viscous shear stress prescriptions, and evolved our models for very long durations of up to $8 \times 10^5 GM/c^3$. Our models resulted in powerful subrelativistic, thermally-driven winds originated from the corona of the accretion flow at distances $10-100 GM/c^2$ from the SMBH. The winds reached velocities of up to $0.01 c$ with kinetic powers corresponding to 0.1-1% of the rest-mass energy associated with inflowing gas at large distances, in good agreement with models of the "radio mode" of AGN feedback. The properties of our simulated outflows are in broad agreement with observations of winds in quiescent galaxies that host LLAGNs, which are capable of heating ambient gas and suppressing star formation.

• The paper shows that thermally-driven winds from RIAF coronae reach speeds up to 0.01 c and contribute 0.1–1% of the inflowing material's rest-mass energy.
• It demonstrates that the mass inflow rate follows a power-law (s up to 2.6), challenging traditional models like ADIOS.
• The simulations suggest these winds heat ambient gas, regulate cooling flows, and suppress star formation, influencing galaxy evolution.

Analysis of SMBH Winds Accreting at Low Rates: Hydrodynamical Exploration

This paper investigates winds and feedback mechanisms in supermassive black holes (SMBHs) that experience low accretion rates. Through comprehensive two-dimensional hydrodynamical simulations, the authors explore radiatively inefficient accretion flows (RIAFs) onto non-spinning black holes, aimed at elucidating the nature and impact of outflows in low-luminosity active galactic nuclei (LLAGNs).

Key Research Methodologies

The simulations employed span a significant portion of parameter space, emphasizing various initial rotation curves and viscous shear stress descriptions. The paper focused on hydrodynamical models over extended durations, reaching up to $8 \times 10^5 GM/c^3$.

Primary Findings

1. Wind Characteristics: The authors identified subrelativistic, thermally-driven wind structures emerging from the corona region, with velocities up to $0.01 c$. The kinetic power associated with these winds was found to account for $0.1-1 \%$ of the rest-mass energy of the inflowing material at larger radii, aligning with "radio mode" models of AGN feedback.
2. Accretion and Outflow Dynamics: The mass inflow rate mirrored a power-law dependence on radius, $\dot{M}(r) \propto r^s$, with values reaching up to $s = 2.6$ in particular simulations, prompting discussions about the applicability of existing theoretical models such as ADIOS.
3. Effect on Host Galaxies: The simulations suggest that winds from RIAFs could play a critical role in galaxy evolution by heating ambient gas, controlling cooling flows, and suppressing star formation. This mechanism supports the observed quiescence in numerous galaxies—potentially explaining the observed properties of the so-called "red geysers."

Comparative Analysis with Previous Studies

The simulated density profiles ($\rho \propto r^{-p}$) were consistent with expectations from the ADIOS paradigm while reporting a significant range in $p$ and $s$ based on model parameters. The insights offered diverge from simple theoretical forecasts suggesting a universal $s$ close to unity for efficient wind production, thus proposing potential adjustments in current models to incorporate diverse initial conditions and physical assumptions.

Future Directions and Implications

The paper lays the groundwork for more sophisticated analyses, potentially exploring the interaction between magnetic fields and hydrodynamic forces. Since magnetic fields remain unaccounted for in the present simulations, the paper acknowledges an avenue for future magnetohydrodynamic (MHD) simulations to enhance the understanding of accretion dynamics around SMBHs. The findings underscore the necessity for theories integrating both hot accretion flow dynamics and SMBH wind feedback to explain cosmic phenomena such as the Fermi bubbles and baryon-cycling in galaxies.

Overall, this paper adds a substantial contribution by not only detailing the mechanics of SMBH wind production under low accretion regimes but also by intersecting its findings with observational insights and broad theoretical contexts within galaxy formation and evolution studies.