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Which mechanism(s) are mainly driving nuclear activity in the centres ofgalaxies is a major unsettled question. In this study, we investigate thestatistical relevance of galaxy mergers for fuelling gas onto the central fewkpc of a galaxy, potentially resulting in an active galactic nucleus (AGN). Torobustly address that, we employ large-scale cosmological hydrodynamicsimulations from the Magneticum Pathfinder set, including models for BHaccretion and AGN feedback. Our simulations predict that for luminous AGN($L_{\rm AGN} > 10^{45} {\rm erg/s}$) at $z = 2$, more than 50 per cent oftheir host galaxies have experienced a merger in the last 0.5~Gyr. These highmerger fractions, however, merely reflect the intrinsically high mergerfractions of massive galaxies at $z=2$, in which luminous AGN preferentiallyoccur. Apart from that, our simulations suggest that merger events are not thestatistically dominant fuelling mechanism for nuclear activity over a redshiftrange $z=0-2$: irrespective of AGN luminosity, less than 20 per cent of AGNhosts have on average undergone a recent merger, in agreement with a number ofobservational studies. The central ISM conditions required for inducing AGNactivity can be, but are not necessarily caused by a merger. Despite thestatistically minor relevance of mergers, at a given AGN luminosity and stellarmass, the merger fractions of AGN hosts can be by up to three times higher thanthat of inactive galaxies. Such elevated merger fractions still point towardsan intrinsic connection between AGN and mergers, consistent with ourtraditional expectation.

Cosmological simulations of black hole growth II: how (in)significant are merger events for fuelling nuclear activity?