Simulating AGN Feedback by Line-driven Winds in Idealized Disc Galaxies

Abstract

Active Galactic Nuclei (AGN) feedback plays a crucial role in galaxy formation and evolution. AGN-driven winds, with large kinetic luminosities found observationally, could significantly impact the galaxies hosting the AGN. Radiation pressure on UV absorption lines is a promising mechanism for driving these winds, whose feedback effect remains to be explored.

In this thesis, I explore how AGN feedback influences the galaxy properties using a state-of-the-art cosmological hydrodynamical code – SWIFT with COLIBRE subgrid physics. I implement a new subgrid model for AGN feedback that couples feedback efficiency with the Eddington ratio by a power-law, based on scaling relations for line-driven winds from the analytical model Qwind. I simulated idelized Milky Way-like galaxies incorporating a black hole (BH), cold gas disc, stellar disc, and hot circumgalactic medium (CGMs) within a static dark matter halo potential. The black hole is assumed to accrete gas at the Bondi rate. I explore the effects of varying BH masses, the slope and the normalization in new coupling efficiency model.

I find that higher BH masses result in greater cumulative AGN energy injection, higher AGN energy injection rates, which in turn lead to lower star formation rates (SFR) and cold gas masses but higher gas outflow rates. When comparing fiducial variable coupling efficiency model with default constant coupling efficiency model, the former one produces weaker AGN feedback, characterized by reduced cumulative AGN energy injection, lower AGN energy injection rates, and significantly smaller coupling efficiencies, but higher accretion rates. This results in faster BH growth, larger SFR and cold gas masses, and lower gas outflow rates, while enhancing BH self-regulation. These effects are due to the coupling effeciency typically being lower in the variable efficiency model. Compared to some previous simulations, our results exhibit weaker AGN feedback and less suppression of SFR.