GASTRO-BH: Effects of a Central Black Hole in GSE-like Dwarf-galaxy Mergers Around Milky Way-like Hosts

Recent evidence points to an intermediate-mass black hole (IMBH) in the most massive globular cluster of the Milky Way, ω Centauri. This globular cluster is commonly associated with the Gaia-Sausage/Enceladus (GSE) dwarf galaxy, the last major merger event of our Galaxy, as its nuclear star cluster remnant. Motivated by this, we investigate whether the interaction between a bright GSE-like dwarf galaxy with stellar mass in the range 10 8.5 -- 10 9.7 solar masses and a Milky Way-like host can either suppress or enhance the growth of a central black hole (BH) during the merger process. To this end, we perform high-resolution N-body and smoothed particle hydrodynamics (SPH) simulations with the ChaNGa framework and a modified, angular-momentum-aware Bondi-Hoyle accretion prescription, considering both isolated dwarf galaxies and merger simulations with different stellar feedback efficiencies. The merger simulations show that the interaction does not halt BH accretion; instead, tidal interactions and gas inflows during pericentric passages strongly enhance accretion, leading to BH mass growth by more than two orders of magnitude in both low- and high-feedback models. The enhanced accretion is accompanied by suppressed star formation in the dwarf galaxy. Our results suggest that mergers similar to the GSE event can efficiently fuel IMBH growth in satellite galaxies rather than suppress it. This may be in tension with the estimated low mass of the proposed IMBH in ω Centauri, but it could provide a mechanism for triggering active galactic nucleus activity in dwarf galaxies.