Abstract
The fates of massive galaxies are tied to the evolution of their central
supermassive black holes (BHs), due to the influence of AGN feedback.
Correlations within simulated galaxy populations suggest that the masses of BHs
are governed by properties of their host dark matter haloes, such as the
binding energy and assembly time, at a given halo mass. However, the full
picture must be more complex as galaxy mergers have also been shown to
influence the growth of BHs and the impact of AGN. In this study, we
investigate this problem by using the genetic modification technique to adjust
the assembly history of a Milky Way-like galaxy simulated with the EAGLE model.
We change the halo assembly time (and hence the binding energy) in the absence
of any disruptive merger events, and find little change in the integrated
growth of the BH. We attribute this to the angular momentum support provided by
a galaxy disc, which reduces the inflow of gas towards the BH and effectively
decouples the BH's growth from the properties of the halo. Introducing major
mergers into the assembly history disrupts the disc, causing the BH to grow
$4\times$ more massive and inject feedback that reduces the halo baryon
fraction by a factor of $2$ and quenches star formation. Merger events
appear to be essential to the diversity in BH masses in EAGLE, and we show that
they can also significantly increase the halo binding energy, potentially
explaining the correlation between these quantities.
Description
Are the fates of supermassive black holes and galaxies determined by individual mergers, or by the properties of their host haloes?
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