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

The supermassive black holes (SMBHs) with mass M > 10 9, M hosted by high-redshift galaxies have challenged our understanding of black hole formation and growth, as several pathways have emerged attempting to explain their existence. The "heavy-seed" pathway eases the problem with the progenitors of these SMBHs having birth masses up to about 10 5 M. Here, we investigate the possibility that a local dwarf galaxy, Leo I, harbors a heavy-seed descendant. Using Monte-Carlo merger trees to generate the merger histories of 1,000 dark matter halos similar to the Milky Way (MW; with a mass of about 10 12 M at redshift z = 0). We search for Leo-like satellite halos among these merger trees, and investigate the probability that the progenitors of some 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, T act, has the largest impact on the number of HSSs. We find HSSs in a fraction 0.7%, 18.1%, and 96.5% of MW-like halos when T act is set to 9,000 K, 7,000 K, and 5,000 K respectively. This suggests that Leo I could be hosting a heavy seed and could provide an opportunity to disentangle heavy seeds from other SMBH formation mechanisms.