AGN feedback in merging galaxies with a smuggle multiphase ISM

We study fast nuclear winds driven by active galactic nucleus (AGN) feedback in merging galaxies using high-resolution hydrodynamics simulations. We use Stars and MUltiphase Gas in GaLaxiEs (smuggle) to explicitly model the multiphase interstellar medium (ISM) and employ subgrid dynamical friction for massive black holes (BHs). Furthermore, we use a super-Lagrangian refinement scheme to resolve AGN feedback coupling to the ISM at $\sim 10-100\,$ pc scales. By comparison between merging and isolated galaxies, with and without AGN feedback, we identify trends in the complex interplay between dynamics, BH fuelling and feedback, and star formation and feedback. We consider three galaxy types: Milky Way analogues, Sbc-type galaxies, and Small Magellanic Cloud (SMC) analogues. The synergy between AGN feedback and merger dynamics is strongest in the Milky Way-like mergers, where the AGN winds are energetically dominant and entrain more gas when the initially thin discs become thick and amorphous during the merger. In contrast, the merger of thicker, vigorously star-forming Sbc galaxies is not strongly impacted by AGN feedback until star formation declines in the post-merger phase. Finally, while the subgrid dynamical friction prescription effectively retains BHs in galactic nuclei during more massive mergers, the clumpy multiphase ISM induces significant wandering of low-mass BHs $\mathrm{(< 10^5\, M_\odot)}$ in the shallow potentials of the SMC-like galaxies. These low-mass BHs wander at distances $\gtrsim 2$ kpc from the galactic centre, yielding negligible BH accretion and feedback. This has implications for Laser Interferometer Space Antenna event rates and present a further challenge to understanding the rapid growth of $z\sim 7-10$ quasars discovered by James Webb Space Telescope.