Description
While there is a mounting observational evidence that intermediate mass black holes (IMBHs) may be important in shaping the properties of dwarf galaxies both at high redshifts and in the local Universe, our theoretical understanding of how these IMBHs grow is largely incomplete. To address this issue, we perform high-resolution simulations of an isolated dwarf galaxy harbouring a $10^4M_\odot$ IMBH at its centre at a peak spatial resolution of $\lesssim 0.01$ pc. Within the fully multi-phase interstellar medium (ISM) we incorporate explicit sampling of stars from the IMF, photoionization, photoelectric heating, individual supernovae explosions as well as a Shakura-Sunyaev accretion disc model to track the evolution of BH mass and spin. We find that a nuclear star cluster (NSC) effectively captures the ISM gas and promotes formation a circumnuclear disc (CND) on scales of $\lesssim 7$ pc. Simultaneously, gravitational torques from the NSC reduce CND angular momentum on (sub-)parsec scales, circularizing the gas onto the $\alpha$-accretion disc and promoting sustained IMBH growth at $\sim 0.01$ of the Eddington rate. While in the innermost regions ($\lesssim 0.5$ pc), star formation is highly suppressed, CND is susceptible to fragmentation, leading to the formation of massive, young stars. Interestingly, despite an in-situ supernova rate of $0.3$ Myr$^{-1}$, the dense CND persists, sustaining BH accretion and leading to a net spin-up. Our study demonstrates the complexity of IMBH accretion with the resolved ISM, and paves the way to next-generation studies where growth of IMBH in full cosmological context can be captured.
