The SEEDZ Simulations: Methodology and First Results on Massive Black Hole Seeding and Early Galaxy Growth

Here we introduce the SEEDZ simulations, a suite of cosmological hydrodynamic simulations exploring the formation and growth of the first massive black holes in the Universe. SEEDZ includes models for Population III star formation, supernovae explosions and the resulting formation of light seed black holes, metal enrichment and subsequent Population II star formation, heavy seed black hole formation, Eddington and super-Eddington accretion schemes as well as black hole feedback. In this paper, we cover the overall methodologies employed and present our current results at z = 15 . Our main result so far is that black holes initially grow faster than their host galaxy, and hence over-massive black holes are a feature of the high-redshift Universe. The fundamental black hole-galaxy relationships we observe at z = 0 (especially the M - M relationship) likely only emerge in more mature galaxies. At high-redshift, that relationship has not yet been established. We find that even at these high redshifts, MBHs can grow from their initial heavy seed mass of $ 10 {}^4$ M up to 10 M. At the high end of our MBH masses, our simulated galaxy M - M relations match the observed high redshift trends i.e. over-massive BHs with M/M. This initial set of simulations will continue to run down to z = 10 , where we will perform a comprehensive comparison of simulated MBH number densities and M - M relations with JWST observations. Further simulations with higher resolution will then follow.