We use the most advanced hydrodynamic simulations of cosmic structure formation to study how galaxies and the supermassive black holes they contain formed and changed over time. This gives us a whole new way to look into how cosmic structures are made and how they change over time. We look at how the dynamics of dark matter, the cooling of radiating gas, the formation of stars, the growth of black holes, and other things change over time, starting with conditions that are consistent with the CDM theory of the universe. We've never seen that happen before. We use a method we came up with by simulating the merging of two separate galaxies to show what the physical properties of black holes are. In this study, we look at: (1) the expected global history of BH mass assembly; (2) the evolution of the local black hole-host mass correlations; and (3) the conditions that allowed the first quasars to grow quickly, as well as the features of their hosts and successors today. We find that the total mass density of BH is very close to estimates based on observations. The density of black hole accretion rates peaks at a lower redshift and changes more quickly at high redshifts than the density of star formation rates. However, the ratio of black hole mass density to stellar mass density changes very little at low redshifts. We find that BH masses are strongly linked to many things about star systems. There is a good match between these correlations and the measured local M mathrmBH,- and M mathrmBH,-M_* relationships. However, depending on the mass range, these correlations may also imply that the normalisation and slope have changed slightly with redshift. Our models also make big black holes at high redshifts when there are long periods of exponential growth in places that fall apart quickly and import a lot of gas. This happens when the areas mentioned above fall apart before they should. Not all of the first supermassive black hole (BH) systems to form are the largest BHs that are still around. Because quasars that start to form later tend to be bigger and heavier than those that start to form earlier.

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