Kavli Affiliate: Debora Sijacki
| First 5 Authors: Stephanie Buttigieg, Debora Sijacki, Christopher J. Moore, Martin A. Bourne,
| Summary:
The co-evolution of massive black holes (BHs) and their host galaxies is
well-established within the hierarchical galaxy formation paradigm. Large-scale
cosmological simulations are an ideal tool to study the repeated BH mergers,
accretion and feedback that conspire to regulate this process. While such
simulations are of fundamental importance for understanding the complex and
intertwined relationship between BHs and their hosts, they are plagued with
numerical inaccuracies at the scale of individual BH orbits. To quantify this
issue, taking advantage of the $(100 , h^{-1},text{cMpc})^3$ FABLE
simulation box, we track all individual BH mergers and the corresponding host
galaxy mergers as a function of cosmic time. We demonstrate that BH mergers
frequently occur prematurely, well before the corresponding merger of the host
galaxies is complete, and that BHs are sometimes erroneously displaced from
their hosts during close galaxy encounters. Correcting for these artefacts
results in substantial macrophysical delays, spanning over several Gyrs, which
are additional to any microphysical delays arising from unresolved BH binary
hardening processes. We find that once the macrophysical delays are accounted
for, high-mass BH merger events are suppressed, affecting the predictions for
the BH population that may be observable with LISA and pulsar timing arrays.
Furthermore, including these macrophysical delays leads to an increase in the
number of observable dual active galactic nuclei, especially at lower
redshifts, with respect to FABLE. Our results highlight the pressing need for
more accurate modelling of BH dynamics in cosmological simulations of galaxy
formation as we prepare for the multi-messenger era.
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