Heavy black hole seed survivors in dwarf galaxies: A case study of Leo I

High-redshift supermassive black holes (SMBHs) have challenged our understanding of black hole formation and growth. The ‘heavy-seed’ pathway eases the problem with the progenitors of these SMBHs having birth masses up to∼105 M. Here, we investigate the possibility that a local dwarf galaxy, Leo I, harbours a heavy-seed descendant. Using Monte Carlo merger trees to generate the merger histories of 1000 dark matter haloes similar to the Milky Way (MW), we search for Leo- like satellite haloes and investigate the probability that the progenitors of these satellites formed a heavy seed. We derive the likelihood of such ‘heavy-seed survivors’ (HSSs) across various formation and survival criteria as well as Leo-similarity criteria. We find that the virial temperature for the onset of atomic cooling and rapid gas infall that yields heavy seeds, Tact , has the largest impact on HSS frequency. We find HSSs in a fraction 0.7 per cent, 18.1 per cent, and 96.5 per cent of MW-like haloes when Tact is set to 9000, 7000, and 5000 K, respectively. For the canonical atomic-cooling threshold ( Tact  8000 K), the HSS fraction is 1per cent , indicating that Leo I hosting a heavy-seed descendant is unlikely under well-motivated physical assumptions. Higher HSS fractions occur only under optimistic and currently unsubstantiated assumptions on Tact . Nevertheless, these results motivate future work that clarifies the possibility of heavy-seed BH formation in pristine haloes with nominal virial temperatures below 8000 K. This may motivate Leo I as a target for disentangling heavy seeds from other SMBH formation mechanisms.