Revealing the driving mechanisms of AGN activity and star formation in cosmological simulations

Scaling relations between supermassive black holes and the stellar bulges of their host galaxies reveal a tight correlation between BH growth and star formation (SF).  Using cosmological hydrodynamic simulations from the Magneticum Pathfinder simulation set as well as cosmological zoom-in simulations, I will demostrate that this coevolution can be understood as a balance between AGN feedback and gas cooling and is thus very sensitive to the underlying sub-grid models used to mimic the physics of AGN and SF within cosmological simulations. This implies not only that the coevolution is self-regulated, depending on these models, but also that AGN and SF activity must be closely correlated. Indeed, our simulated AGN light-curves and the SF history follow very similar trends. However, AGN act on much shorter time scales than SF and the two can be shifted against each other in time. In agreement with recent observations, detailed AGN light- curves also reveal that most simulated AGN are not driven by galaxy mergers, but by smooth or clumpy gas accretion, or by internal processes. This strongly challenges the traditional view, in which AGN and starbursts are mainly driven by mergers.