Speaker
Description
Some recent cosmological simulations have started to model the dynamics of supermassive black holes (SMBHs) with dynamical friction subgrid models instead of repositioning. Such simulations predict a population of wandering black holes in massive galaxies, with the most massive systems including more than a thousand wandering black holes. We run a series of cosmological zoom-in simulations with different halo mass thresholds for black hole seeding, and study how the population of black holes is affected. A dynamical friction subgrid model is used for seed-mass SMBHs. Larger SMBHs are modelled using the algorithmic regularization code KETJU, which is able to model SMBH binaries down to separations where gravitational wave emission drives binaries to coalescence. The effect of seeding threshold on central SMBHs is small, with all grown central SMBHs following an observed SMBH mass - galaxy stellar mass relation. The seeding criteria heavily affects the population of wandering black holes, as the number of black holes in the most massive galaxies varies by an order of magnitude between the simulations. The number of SMBH mergers also changes by a significant amount, highlighting the need of accurate seeding prescription for constraining the merger rate prediction for the LISA space mission.