Unveiling the first seeds of supermassive black holes using cosmological simulations*

Supermassive black holes are now believed to be at the centers of almost every massive galaxy in our Universe. Where and how did they form and grow to their observed masses (a million to tens of billion solar masses)? Unveiling the nature of their first "seeds" is a key science goal for current and future observational facilities such as JWST, LISA and Lynx. Predictions from cosmological hydrodynamic simulations are going to be crucial for using data from upcoming facilities to determine seeding mechanisms. However, current cosmological simulations cannot constrain seed formation because they are unable to properly resolve the seeds and their formation processes. I will talk about our recent works geared towards developing seeding prescriptions for the next generation cosmological simulations. Unlike current state of the art, these simulations would be able to distinguish between black holes originating from different seeding mechanisms. To start with, we have conducted a large systematic study using the highest resolution "zoom-in" cosmological simulations, which explores a range of black hole seeding prescriptions that depend on the gas properties within dark matter haloes. We seed black holes in nearly pristine star forming halos and investigate the impact of changing the minimum halo mass and star forming, metal poor gas mass thresholds on key observables such as black hole merger rates, masses and luminosities. The different seeding conditions leave strong and distinct imprints on the merger rates measurable by LISA. However, electromagnetic observations alone may find it difficult to discriminate between seeding channels. Finally, I will also discuss implications of our seeding models on the assembly of the highest redshift (z > 6) quasars. Overall, these results are going to provide a useful benchmark for continued development of black hole seeding prescriptions for large volume cosmological simulations.