2024MNRAS.528....1H

We investigate how the properties of massive black hole binaries influence the observed properties of core galaxies. We compare the observed trend in stellar mass deficit as a function of total stellar mass in the core galaxy with predicted trends in IllustrisTNG. We calculate mass deficits in simulated galaxies by applying subgrid, post-processing physics based on the results of literature N-body experiments. We find that the median value of the posterior distribution for the minimum binary mass ratio capable of creating a core is 0.7. For the gas mass fraction above which a core is erased, we find a median value of 0.6. Thus, low mass ratio binaries do not contribute to core formation and gas-rich mergers must lead to star formation within the nucleus, ultimately erasing the core. Such constraints have important implications for the overall massive black hole binary population, black hole-galaxy co-evolution, and the origin of the gravitational wave background.