The importance of nuclear star clusters for massive black hole growth and nuclear star formation in simulated low-mass galaxies

Abstract: Observed low-mass galaxies with nuclear star clusters (NSCs) can host accreting massive black holes (MBH). We present simulations of dwarf galaxies ($M_{\mathrm{baryon}} \sim 0.6 - 2.4 \times 10^8 \rm \, M_\odot$) at solar mass resolution ($0.5\rm \, M_\odot < m_{\mathrm{gas}} < 4 \rm \, M_\odot$) with a multi-phase interstellar medium (ISM) and investigate the impact of NSCs on MBH growth and nuclear star formation (SF). The Griffin simulation model includes non-equilibrium low temperature cooling, chemistry and the effect of HII regions and supernovae (SN) from massive stars. Individual stars are sampled down to 0.08 $\rm M_\odot$ and their non-softened gravitational interactions with MBHs are computed with the regularised Ketju integrator. MBHs with masses in the range of $10^2 - 10^5 \, \rm M_\odot$ are represented by accreting sink particles without feedback. We find that the presence of NSCs boost nuclear SF (i.e. NSC growth) and MBH accretion by funneling gas to the central few parsecs. Low-mass MBHs grow more rapidly on $\sim 600$ Myr timescales, exceeding their Eddington rates at peak accretion. MBH accretion and nuclear SF is episodic (i.e. leads to multiple stellar generations), coeval and regulated by SN explosions. On 40 - 60 Myr timescales the first SN of each episode terminates MBH accretion and nuclear SF. Without NSCs, low-mass MBHs do not grow and MBH accretion and reduced nuclear SF become irregular and uncorrelated. This study gives the first insights into the possible co-evolution of MBHs and NSCs in low-mass galaxies and highlights the importance of considering dense NSCs in galactic studies of MBH growth.