Simulating AGN Feedback
Active Galactic Nuclei (AGN) exert powerful influence on their host galaxies. These feedback processes regulate star formation, impact gas inflows, and shape the co-evolution of galaxies and supermassive black holes (SMBHs). To explore this, we conduct the following projects.
Simulating variable coupling efficiency in idealized disky galaxy
Most large-volume cosmological simulations treat AGN feedback using simplified prescriptions with constant coupling efficiency — the fraction of AGN luminosity converted to kinetic energy. However, observations and small-scale accretion-disc models (especially UV line-driven wind models) suggest that the coupling efficiency might depend strongly on the black hole accretion rate, typically following a power law.
In this project, we introduce a new AGN feedback model where the coupling efficiency varies with the Eddington ratio, motivated by UV line-driven wind model, and study its impact on disc galaxy evolution.
Our simulations use the SWIFT hydrodynamic code with the COLIBRE galaxy formation model. We construct idealised Milky Way-like galaxies including: a static dark matter halo, a stellar disc, a cold gas disc, a hot circumgalactic medium, and a central SMBH
Only the thermal AGN feedback is turned on, and we implement the variable coupling efficiency by the following equation
\[ \eta = \min(N_\eta \, \dot{m}^{\alpha_\eta}, 1) \]where: \(\dot{m}\) is Eddington ratio. \(N_\eta, \alpha_\eta\) are normalization and slope, respectively, which are free parameters. The fiducial model is \(\eta \propto \dot{m}^{2.6}\). Additionally, we test variations in slope and normalization by \(N_\eta = 10, 300, 3000\) while fixing slope as 2.6, or \(\alpha_\eta = 0.5, 1.5, 3.0\) but requiring \(\eta = 0.1\) when \(\dot{m} = 0.1\). The figure showing how \(\eta\) vary with \(\dot{m}\) is attached below.
The main results are